The goshawk Accipiter gentilis has recently been reintroduced into parts of Great Britain. During the course of a study of one population, lesions of stomatitis were observed in 14 young from five broods and all the affected birds died. Postmortem examination of three birds revealed live Trichomonas gallinae in exudate from one, and histological findings consistent with a diagnosis of trichomoniasis were made in this and one other bird. It is suggested that trichomoniasis may be a significant mortality factor in goshawks from Britain.