This study aimed to investigate the prevalence of otomycosis and aetiological agents in Khouzestan province, south-west Iran. This cross-sectional study examined and cultured 881 swabs from suspected external otitis cases, collected from throughout Khouzestan province. Fungal agents were identified by slide culture and complementary tests when necessary. The mean patient age was 37 years. The 20-39 year age group had the highest prevalence of otomycosis: 293 cases, comprising 162 (55.3 per cent) women and 131 (44.7 per cent) men. The seasonal distribution of cases was: summer, 44.7 per cent; autumn, 28.7 per cent; winter, 14.7 per cent; and spring, 11.9 per cent. The fungal agents isolated were Aspergillus niger (67.2 per cent), Aspergillus flavus (13 per cent), Candida albicans (11.6 per cent), Aspergillus fumigatus (6.2 per cent) and penicillium species (2 per cent). Fungal otomycosis is still one of the most important external ear diseases. In this study in south-west Iran, Aspergillus niger was the predominant aetiological agent. However, clinicians should be cautious of candidal otomycosis, which has a lower rate of incidence but is more prevalent among 20-39 year olds.