The present study investigated the effects of slow-release implants containing the gonadotrophin-releasing hormone (GnRH) agonist deslorelin on reproduction in the common brushtail possum (Trichosurus vulpecula). Captive female brushtail possums were assigned to control (placebo implant), low dose (4.7 mg deslorelin) or high dose (9.4 mg deslorelin) groups; males were assigned to control or high dose (9.4 mg deslorelin) groups. The acute effects of deslorelin treatment at the level of the pituitary gland were similar between the two sexes, where a transient rise in luteinising hormone concentration was induced over the first 24 h. In females, this was associated with the disruption of the normal oestrous cycle and mating within 2–10 days in some treated individuals, but no young were subsequently detected. By 3 weeks after treatment, treated females became anoestrus and remained infertile for at least one breeding season. The effects of treatment were reversible in a subset of females that had their implants removed, although the time taken to produce offspring was variable. Paradoxically, male brushtail possums remained fertile during chronic deslorelin exposure. Despite significant declines in basal follicle-stimulating hormone and testosterone concentrations, as well as an inability to respond to a GnRH challenge, treated males sired as many offspring as control males and there was no evidence of testicular regression. In conclusion, there is potential to control reproduction in female brushtail possums by using chronic GnRH agonist treatment.