The diagnostic and prescribing habits of general practitioners from 17 European countries for 4094 patients with acute tonsillitis were assessed, and differences in outcome were identified. At least 10 general practitioners from each country filled in a questionnaire for each episode of acute tonsillitis treated during a three month period, November 1989-May 1990. Differences in days of fever and illness were tested by one-way analysis of variance. Bacteriological tests were rarely used for diagnosis in East Germany, Poland and the Netherlands, while a high percentage (70-96%) occurred in Turkey, Romania, Israel, Yugoslavia, Finland and Greece. Group A beta-haemolytic streptococci (40 per cent) and a negative test result (43 per cent) were the most common results. Ninety per cent or more patients were treated with an antibiotic. Oral penicillin was especially prescribed in the northern countries of Europe and parenteral penicillin in southern Europe. For almost all countries the mean number of days with fever was between 2 or 3 days. The mean number of days with illness differed greatly (F = 62.12; P = 0.0000). Turkey had the lowest mean (2.56), while Poland had the highest mean (8.23).