| Cașin | |
| Pushpin Map: | Romania |
| Subdivision Type1: | Country |
| Subdivision Name1: | Romania |
| Subdivision Type2: | Counties |
| Subdivision Name2: | Bacău County |
| Subdivision Type3: | Villages |
| Subdivision Name3: | Mănăstirea Cașin, Lupești, Cașin, Onești |
| Length: | 54km (34miles) |
| Mouth: | Trotuș |
| Mouth Location: | Onești |
| Mouth Coordinates: | 46.259°N 26.7652°W |
| Basin Size: | 308km2 |
The Cașin is a right tributary of the river Trotuș in Romania.[1] It discharges into the Trotuș in Onești.[2] Its length is 54km (34miles) and its basin size is 308km2.
The following rivers are tributaries to the river Cașin (from source to mouth):