Buprenorphine has recently obtained UK Marketing Authorisation for horses. The analgesic effects are long lasting, and have considerable potential for postoperative pain relief. This observer blinded, randomised study aimed to evaluate postsurgical analgesia in ponies premedicated with buprenorphine prior to castration under intravenous anaesthesia. Ponies received either 0.01 mg/kg bodyweight (BW) buprenorphine (group B) or an equivalent volume of 5 per cent glucose (group C) given intravenously before induction of anaesthesia. Pain was assessed and recorded using dynamic interactive visual analogue scores (DIVAS 0–100) and a Simple Descriptive Scale (SDS 0–3) (high scores=most pain) before and 1, 3, 6, 9, 12 and 24 hours after anaesthesia. Rescue analgesia was given if DIVAS>40 mm. Data were analysed using the Mann-Whitney U test at P<0.05. Median (range) areas under the curve for DIVAS were 63 (0–383) mm hour in group B and 209 (0–391) mm hour in group C (P=0.0348). The SDS was lower in group B than in group C (P=0.038). Three group B and five group C animals required rescue analgesia. Buprenorphine did not produce any serious adverse effects. Buprenorphine at 0.01 mg/kg BW intravenously administered before anaesthesia provided near-comprehensive postoperative analgesia after surgical castration in ponies.