This study clearly shows that hepatitis E virus (HEV) was the major aetiological virus in an outbreak in the south of Morocco, in 1994. Acute hepatitis E was diagnosed using recombinant antigen-based enzyme immunoassays and reverse transcription polymerase chain reaction in 77.3% of patients. In the west of Morocco, 6.1% of controls were positive for anti-HEV IgG. The anti-HEV prevalence in patients was significantly higher than that of controls (84.0% vs. 6.1%) (P < 0.001). In healthy contacts residing in southern Morocco, 10.4% had anti-HEV IgG, indicating past HEV infection. Furthermore, HEV-specific IgM was associated with subclinical HEV infection in 9 contacts and was noted in 10 others who were convalescent. Faecal contamination of drinking water samples collected from the epidemic city was observed. It also appeared that primary infection with HEV accounted for more than 86% of the cases. A longitudinal study showed waning of anti-HEV antibodies in patients and healthy contacts six months after the initial testing. Subclinical HEV infection was significantly prevalent in a paediatric population younger than 10 years (P < 0.05). Our results also showed that anti-HEV IgG in healthy contacts decreased significantly after 30 years of age (P < 0.01), whereas the clinical acute HEV infection incidence increased significantly with age (P < 0.01). From this study, it appears that HEV is present in both the west and the south of Morocco.