More patients were hospitalised for acute salpingitis at the Department of Obstetrics and Gynaecology, Orebro Medical Centre, Orebro, Sweden, during the 5 year period 1970-1974 (period I) as compared with that of 1980-1984 (period II), 666 patients and 524 respectively, a decrease of 22%. The majority of cases, 92% in period I and 85% in period II, occurred among women 15-34 years of age, that is a relative increase of patients aged over 34 from 8% in period I to 15% in period II. Concomitant urogenital gonorrhoea occurred in 26.2% of the patients in period I compared with 12.0% in period II, a highly significant decrease (p less than 0.001) mainly confined to the age group 15-24, whereas there was no relative difference for the two periods in the age group 25-34 years. The number of patients using intrauterine contraceptive device (IUCD) was 96/666 (14.4%) in period I compared with 113/524 (21.6%) in period II (p less than 0.001). There were also relatively more IUCD users among the patients with gonorrhoea and acute salpingitis in period II (15.5%) compared with period I (10.4%) but this difference was not statistically significant. From 1981 to 1984 370/424 patients were cultured for Chlamydia trachomatis and 27.8% (103/370) were positive. Thus Chlamydia trachomatis is at present, at least in the Orebro area, the most frequently isolated STD agent among acute salpingitis patients while gonorrhoea is of much less importance.