Diagnosis of gonorrhoea indicates that relatively recent unprotected sex has been practised and thus there is possibly a risk of HIV transmission. A retrospective analysis of gonorrhoea cases reported to the Danish national surveillance system was carried out for the period 1994-1999. The analysis included demographic pattern and mode of transmission of gonorrhoea in Denmark with the focus on trends and factors related to infection in men who have sex with men (MSM). We found that 646 (82.7%) reported cases of gonorrhoea were men, among whom 41.2% cases were due to sex with men, 52.9% were transmitted by heterosexual contact and 5.9% were due to unknown causes. The estimated mean annual reported incidence of gonorrhoea was more than 30 times greater among MSM than among heterosexual men and 6 times greater in MSM known to be HIV-positive, when gonorrhoea was diagnosed, than among other MSM (p < 0.001). No difference was found between the sites of infection among HIV-positive and HIV-negative MSM. A trend towards increase in the annual incidence of gonorrhoea has been seen since 1997, with an increase of 35% from 1997 to 1998 and a further increase of 41% from 1998 to 1999. The increase was mainly due to an increasing number and proportion of cases among MSM. The notified cases comprised 49% of patients with laboratory-confirmed gonorrhoea, which indicates a similar increasing trend. In conclusion, the rising trend of incident gonorrhoea, especially in MSM, may indicate a relapse to more unsafe sexual practices, which could lead to the spread of HIV infection. The higher incidence among HIV-positive MSM compared with other men underlines this concern.