This study describes 10 tomcats with different reproductive disorders. Two of the cats had abnormal sex chromosomes; one was a tortoiseshell and white Cornish rex, while the other was a brown Burmese. The other eight cats were diagnosed as having testicular hypoplasia, diphallos in combination with unilateral cryptorchidism, a persistent penile frenulum, retrograde ejaculation, temporary oligozoospermia, teratozoospermia, azoospermia and congenital poor libido. For the cat with a persistent penile frenulum, and the cat with a temporary oligozoospermia, the prognosis for successful reproduction was considered favourable. By contrast it was considered unlikely that the cats with chromosomal abnormalities, testicular hypoplasia, diphallos, retrograde ejaculation, teratozoospermia and azoospermia would be able to produce offspring.