Extraintestinal manifestations of inflammatory bowel disease (IBD) are commonly observed in humans but are poorly documented in companion animals. Thrombocytopenia is an uncommon but well-documented extraintestinal hematological abnormality in humans; however, there are no previous reports of IBD and concurrent thrombocytopenia in the veterinary literature. Seven dogs having idiopathic IBD and concurrent thrombocytopenia were identified and evaluated retrospectively (this represents an incidence of 2.5% in the authors' IBD population). Obvious known causes for thrombocytopenia were eliminated by diagnostic testing as deemed appropriate by the clinician of record. Thrombocytopenia resolved with treatment for the IBD in some but not all patients. This is similar to reports in humans. Thrombocytopenia typically appears to be subclinical, and the severity does not correlate with the degree of intestinal inflammation defined histopathologically. However, quantitative platelet counts should be monitored during IBD therapy, as additional immunosuppression may be required to treat thrombocytopenia, despite resolution of gastrointestinal signs. It is speculated that thrombocytopenia may be causally associated with canine IBD, possibly secondary to immune stimulation from lumenal bacterial antigens, altered immunological regulation, or both.