Many factors affect the cure rate (CR), duration required for complete cure (DC) and the recurrence rate (RR) of onychomycosis. The aim of this study was to evaluate the CR, DC and RR in onychomycosis according to various clinical factors. We retrospectively reviewed medical records of 637 Korean patients with onychomycosis between December 2000 and December 2006. We examined six clinical factors to evaluate the effects on the CR, DC and RR: age, sex, clinical type, treatment pattern, presence of diabetes mellitus (DM) and the extent of nail involvement. On the view of the clinical nail appearance and potassium hydroxide (KOH) preparation, we designated the CR, DC and RR. In addition, we examined the differences in the CR, DC and RR in terms of the above-mentioned clinical factors. A total of 207 eligible patients were finally analysed. The CR as a whole was 78.3%, the DC was 31.7 ± 18.4 weeks and the RR was 36.0%. There were significant differences in the CR, DC and RR according to the extent of nail involvement. Age affects the CR and DC, and DM also affects the DC and RR. We found that the extent of nail involvement, age and DM affect the CR, DC and RR of onychomycosis.