To determine the incidence and describe the complications of laparoscopic procedures in The Netherlands. A nationwide prospective multicentre observational study. Data on complications were registered from 1 January to 31 December 1994 by 72 hospitals. Any unexpected or unplanned event requiring intra-operative or post-operative intervention was defined as a complication. Complications were classified in two groups: approach and technique related complications. Complication rates were compared with these already published. Of 25,764 laparoscopic procedures, 145 complications occurred (rate 5.7 per 1000 [/1000]); two deaths occurred. In 84 women laparotomy was necessary (rate 3.3/1000). In 83 cases (57%; 95% CI for approach = 49-65%) the complication was caused by the surgical approach; in 62 cases (43%) the technique was at fault. Haemorrhage of the epigastric vein and intestinal injury, often requiring laparotomy (90% of cases) were the most frequently observed complications. The complication rate was 2.7/1000 for diagnostic laparoscopic procedures, 4.5/1000 for sterilisation and 17.9/1000 (chi 2 = 127; dF = 2; P < 0.001) for operative laparoscopy. The highest incidence was registered for complications occurring during laparoscopic (assisted) hysterectomy. Stepwise logistic regression analysis showed that previous laparotomy and surgical experience were associated with complications requiring laparotomy. Most complications occurred during operative laparoscopic procedures (rate 17.9/1000). Residents in training are required to learn diagnostic laparoscopy and sterilisation and this training programme results in a fall in the risk of the complications. However, operative laparoscopic procedures are still hazardous, especially laparoscopic hysterectomy. Women with a previous laparotomy are particularly at risk.