The Cașin is a right tributary of the river Trotuș in Romania. It discharges into the Trotuș in Onești. Its length is 54 km (34 mi) and its basin size is 308 km (119 sq mi).

Tributaries

The following rivers are tributaries to the river Cașin (from source to mouth):

• Left: Dobrii, Bucieș, Curița
• Right: Zboina, Marmora, Haloșul Mic, Haloșul Mare, Haloșul Ciubotaru, Buciumi