Route 90 is a state highway in McDonald and Barry counties in southwest Missouri, United States, that connects Missouri Route 43 (Route 43) in Southwest City with Missouri Route 37 (Route 37) in Washburn.
For its entire length Route 90 is a two-lane highway. It passes through rugged areas and the roadway is both very hilly and very curvy.
Route 90 begins an intersection with Route 43 in the extreme northeastern part of the city of Southwest City. (From that intersection northbound Route 43 heads north towards Seneca and southbound Route 43 heads briefly west, then south through Southwest City and then on towards Maysville and Siloam Springs, both in Arkansas. Also from that intersection, County Road 9097 heads south, then southwest to end at Route 43.)
From its western terminus, Route 90 proceeds east for nearly before turning north-northeast and connecting with the north end of Route MM at a T intersection. (Route MM heads southeasterly towards the unincorporated community of Pack and then on to the Arkansas state line.) Route 90 continues north-northeasterly for just over before turning easterly again. After about Route 90 enters the city of Noel and immediately connects with the south end of Route TT at T intersection in a part of the city that was formerly the unincorporated community of Spring Valley.
Approximately further southeast Route 90 reaches its western junction with Missouri Route 59 (Route 59) at a T intersection on the south bank of the Elk River. (Route 59 heads north along North Cliffside Drive to cross the Elk River and then on towards Lanagan.) Route 40 proceeds southeast, concurrently with Route 59 for roughly before reaching its eastern junction with Route 59 at another T intersection. (Route 59 heads south towards Sulphur Springs and Siloman Springs, both in Arkansas.) After crossing over Butler Creek and then proceeding easterly for a little more than another , Route 90 connects with the west end of Route H at Kings Highway. (While South Kings Highway heads south to end near the south end of Noel, Route H [North Kings Highway] heads northeasterly towards Interstate 49 / U.S. Route 71 [I-49 / US 71] and Pineville.) Route 90 the proceeds south-southeast and leaves Noel shortly thereafter.
After continuing for south-southeast for a little more than Route 90 turns to proceed easterly. Approximately later Route 90 crosses Mill Creek and about after the creek crossing Route 90 reaches I-49 at a diamond interchange, I-49 exit 2. (I-49 heads north to run concurrent with US 71 and then on towards Pineville, Joplin, Kansas City. I-49 heads south towards Bentenville, Fayetteville, and Fort Smith, all in Arkansas.)
Roughly east of I-49, and just after entering the village of Jane, reaches US 71 at an at-grande junction. (I-49 heads north to run concurrent with I-49 and then on towards Pineville, Joplin, and Kansas City. US 71 heads southeasterly towards Bella Vista and Bentonville, both in Arkansas.) Just under a farther east, Route 90 reaches County Road 7137 (Raines Road) at a T intersection. (Rains Road is the former routing of US 71 and it heads south to connect with US 71, via Meadowlark Lane, farther south in the village.) Route 90 the turns northerly to run along Rain Road for approximately before turning easterly. (Raines Road, the former routing of US 71, continues northwesterly to end at U.S. Route 71 Business. Shorty Holland Lane heads very briefly west from that intersection as well.) Proceeding northeasterly, Route 90 leave Jane a little more than later.
Roughly east of Jane, Route 90 crosses Little Sugar Creek and the connects with the south end of Route K about later. (Route K heads westerly to end at U.S. Route 71 Business. Malcom Lane heads very briefly north from that intersection as well.) Route 90 then proceeds along east-southeasterly course for just over , passing through the unincorporated community of Arnett along the way. Route 90 then proceeds east-northeasterly for just over before reaching its junction with Route E at an unual intersection. (Route E heads north towards Powell and south towards Pea Ridge.) East of Route E, Route 90 continues east-northeasterly for about to connect with the north end of Route KK at a T intersection. (Route KK heads south towards Jacket.) Beyond that intersection Route 90 turns northerly and promptly crosses Big Sugar Creek. After briefly continuing northerly and crossing Trent Creek, Route 90 turns to proceed easterly again for to pass through the unincorporated community of Cove, cross Trent Creek for a second time, and leave McDonald County to enter Barry County.
Just over east of the county line, Route 90 connects with the north end of Route NN at a T intersection. (Route NN heads south toward Mayflower.) From that intersection, Route 90 proceeds northeasterly for before connecting with the south end of Route UU at a T intersection. (Route UU heads northwesterly toward the Flag Spring Conservation Area.) From its junction with Route UU, Route 90 proceeds southeast for just of over before turning due east and entering the city of Washburn, just under later. Near the eastern edge of Washburn, Route reaches its eastern terminus at Route 37 at a T intersection. (Route 37 heads north towards Cassville, Monett, and Sarcoxie. Route 37 heads south towards Seligman, the Arkansas state line, and Gateway in Arkansas.)
Route 90 was one of the original 1922 state highways. Its eastern terminus was at Missouri Route 1 in Noel and its western terminus was at the corner of Missouri, Oklahoma, and Arkansas near Southwest City. It was eventually extended down Routes P and K to Washburn.