Otoyol 21A, abbreviated as O-21A, is a 32 km (20 mi) long auxiliary otoyol connecting the D.330 and D.750 to the O-21. The motorway was opened in 1992 as a connecting route to Konya and passes through mostly uninhabited rural land. The O-21A is a part of the E90.

The motorway was deemed too short to receive its own O-XX designation, despite being longer than the O-50, but too long to be designated as an exit; therefore, the route was signed as the O-21A, and is the only otoyol route in Turkey to have an alpha-numeric route designation.

Province	District	km	mi	Exit	Destination	Notes
Konya	Ereğli	0.0	0.0	-	D.330 — Konya	Continues as the D.330
		0.6	0.4	K153	D.750 — Zonguldak, Tarsus
Niğde	Ulukışla	17.6	10.9	K152	D.805 — Niğde, Ulukışla
		28.8	17.9	K151	Eminlik
		30.1	18.7	Eminlik Toll Plaza
		32.3	20.1	K15	O-21 — Niğde, Tarsus

Light blue indicates toll section of motorway.

• List of highways in Turkey

• Mersin Diyarbakır road map Archived 2011-07-25 at the Wayback Machine