Contraception is an essential tool for controlling reproduction in captive and free-ranging lions. This paper describes the treatment and contraception of 23 captive and 40 free-ranging lionesses ( Panthera leo ) and four captive tigers ( Panthera tigris ) in South Africa using 3 × mg, 2 × mg, mg or + mg deslorelin implants. Thirty-one lionesses were treated more than once at 11- to 60-month intervals. In Brazil, two lionesses were treated with -mg implants and faecal progesterone and oestradiol concentrations were monitored for 920 days. All combinations of deslorelin showed the length of contraception to be around 30 months with one 3 × mg treatment lasting 40 months in one captive lioness. The mean time taken to reconception was months for the 3 × mg combination. The faecal analyses of the lionesses in Brazil reflected quiescent ovarian activity for periods of 17 and 30 months, respectively, when small oestradiol peaks but no progesterone peaks started to appear. This confirmed the field observations in South Africa. No side effects occurred although several of the lionesses were treated repeatedly for up to 8 years. Deslorelin (Suprelorin) is a safe and effective means of controlling reproduction in captive or free-ranging populations of lions. Where contraception is to be maintained, the implementation of implants at 24-month intervals is recommended.