Summary.The identification of infrequent side‐effects of clotting factor concentrates, undetected by clinical trials, is facilitated by post‐marketing surveillance. We present a post‐marketing surveillance study in which 97 patients with haemophilia A, attending three haemophilia centres, were treated over a median follow‐up period of 284 days (range 1–1074), and a total follow‐up period of 30,080 days, with a pasteurized immunoaffinity purified factor VIII concentrate (Monoclate‐P, Armour, Collegeville, USA). 5216 infusions, using 10,527,000 units of Monoclate‐P, were carried out, mostly for routine haemarthroses or prophylaxis.No new inhibitors were observed during the study. At the start of the study 60/97 were HIV seropositive, 67/97 HBs antibody positive, 12 HbsAb negative and the remainder HBsAb positive before the study period. 13/14 tested were HAV seropositive at the beginning of the study. One patient became HAV seropositive during the study period, an infection thought to be community acquired. No other seroconversions were observed. Only one mild transfusion reaction was observed. This study confirms the safety and efficacy of Monoclate‐P. Post‐marketing surveillance or nationally organized pharmaco‐vigilance should be practiced more widely to enable identification of low‐frequency si