Fourteen female cats with fibroadenomatosis were treated with aglepristone, and the effectiveness of the treatment and its effect on selected haematological and blood chemistry parameters were studied. The cats were monitored for 12 months after the end of the treatment. Complete remission of the clinical signs was achieved on average 3·9 weeks after the treatment began; the success of the treatment confirmed the clinical diagnosis of fibroadenomatosis. During the course of the treatment the cats’ haematological parameters returned to normal. In cats that had previously been treated with longacting medroxyprogesterone acetate, treatment with aglepristone for five weeks was recommended. Cases of fibroadenomatosis reappearing after a few months should be regarded as new disease rather than a relapse. Six cats were subsequently mated and four gave birth to one or more litters; all the pregnancies proceeded normally with no clinically evident fibroadenomatosis. The other eight cats underwent ovariohysterectomy soon after the aglepristone treatment was completed.