In 15 years at Bristol there have been 293 cases of torsion of the testis, 55 cases of torsion of a testicular appendage and 5 cases of testicular ischaemia due to other causes. The risk of a male developing torsion of the testis or its appendix by the age of 25 is about 1 in 160. Both conditions occurred primarily in adolescents, but among prepubertal boys torsion of an appendage was as common as torsion of a normally descended testis. There was a slight left-sided preponderance in testicular torsion, more marked in torsion of the appendages; the incidence of bilateral torsion was 2-0 and 1-8 per cent respectively. The clinical features and differential diagnosis of the two conditions are compared. Torsion of a testicular appendage is the most commonly misdiagnosed scrotal lesion, the preoperative diagnosis being correct in only 11 per cent of cases compared with 90 per cent for torsion of the testis. Twenty-one cases of recurrent torsion underwent prophylactic bilateral orchidopexy. There were 20 cases of torsion of undescended testes, with a salvage rate of only 20 per cent. The overall testicular survival rate was 55-3 per cent. Viability depends upon the possibility of spontaneous reduction, the preoperative delay after the onset of symptoms, the degree of torsion of the cord and the length of follow-up in doubtful cases. Urgent scrotal exploration is advised in every case of acute testicular pain unless there is overwhelming evidence of epididymoorchitis. Exploration of the opposite side is mandatory in torsion of the testis and advisable in torsion of an appendage.