The association of Aeromonas spp. with travellers' diarrhoea was studied among 978 Finnish tourists travelling to Morocco in winter (n = 398) and autumn (n = 580) in 1989. Fifty-five isolates from diarrhoeal patients with (n = 16) or without (n = 39) a recent travelling history in a developing country were also included. In Morocco, Aeromonas spp. were isolated from 8.7% of patients with diarrhoea and from 1.4% of non-diarrhoeal tourists (p < 0.001). Aeromonas spp. were found as the sole pathogen in 5.5% of patients (p < 0.001). Diarrhoea with multiple pathogens, including Aeromonas spp., was found in 3.1% of patients. Species identification by phenotypic and genotypic methods indicated that A. veronii biotype sobria (hybridisation group HG 8/10) and A. caviae (HG 4) were the most common Aeromonas spp. associated with travellers' diarrhoea. A. hydrophila (HG 1) and A. caviae (HG 4) were common in patients acquiring diarrhoea in Finland. Ribotyping of strains within a species showed that all strains had different ribotypes although the tourists were infected during the same trip. This study suggested that only certain Aeromonas spp. were commonly found in travellers' diarrhoea. However, the causative role of those species is unclear.