Few studies have examined the prevalence of onychomycosis among diabetic patients. Given the morbidity linked to onychomycosis, and the ever-growing size of the diabetic population, a better recognition of this nail infection is welcome. To revisit the relative prevalence of dermatophyte, yeast and non-dermatophytic mould onychomycoses in diabetic adults in a prospective study using combined histomycology and cultures. Toenail clippings were collected for 3 years in 190 type II diabetic patients (136 men and 54 women) and from an age- and gender-matched group of non-diabetic subjects. All sampled nails showed clinical alterations reminiscent of onychomycosis. Histomycology and cultures were performed on each sample to distinguish onychomycosis from non-infectious onychodystrophy. Compared to non-diabetic subjects with nail alterations, diabetics showed a higher proportion of onychomycosis relative to non-fungal onychodystrophy. Diabetic men suffered more frequently from onychomycosis and onychodystrophy than diabetic women. When considering the nature of the fungal pathogens, dermatophytes predominated largely over yeast and non-dermatophytic moulds, both in diabetic and non-diabetic patients. Diabetic patients, particularly men, are at increased risk of developing onychomycosis. The morbidity linked to this disorder, and its impact on the foot status in diabetic subjects merit to be better appreciated by clinicians.