Sixteen of 65 laparoscopically assisted colorectal operations were converted to an open procedure, usually because of dissection difficulties. Conversion was decided early in the procedure in four cases without perioperative morbidity and later in 12 cases, after a mean of 56 min. The results in patients undergoing converted operation were compared with those in 252 having a planned open colorectal procedure during the same period. The groups were comparable with regard to age, health status, factors influencing intestinal healing and grade of surgeon. A higher postoperative morbidity rate (50 versus 21 per cent) and more anastomotic leakages (25 versus 8 per cent) were apparent in the converted group. Operating time, postoperative ileus and hospital stay were longer in those requiring a converted operation. These poor results suggest that careful preoperative patient selection for laparoscopic procedures and a rapid decision to convert in case of difficulty are important.