In the current study, the duration of effectiveness, owner satisfaction and side effects of a gonadotrophin releasing hormone-agonist (deslorelin) implant were investigated during a two-year follow-up study in which 61 male and 69 female entire pet ferrets were given a 4.7 mg deslorelin implant as alternative to surgical neutering. In 27 participating non-oestrous jills, a double-blind placebo controlled study was performed to investigate whether a single low dose of medroxyprogesterone (2 mg orally) four days preceding placement of the implant could prevent oestrus induction. The duration of effectiveness of the implant ranged from 301 days to over 1339 days (mean 1012±38 days), with no sex difference present. Over 90 per cent of owners were pleased with the effects of the implant. Minor local side effects were noted in less than 20 per cent of ferrets, which all resolved within a week without treatment. Oestrus was induced in 77 per cent of jills receiving medroxyprogesterone and 50 per cent of jills receiving the placebo, indicating that administration of a low-dose progestogen cannot prevent postimplant oestrus. Based on the minimum duration of effectiveness, it is advised to place a new implant on a yearly basis to guarantee continuous gonadal suppression, although biannual replacement may be sufficient in the majority of ferrets.