Background/Aim: Onychomycosis (OM) is one of the commonest superficial fungal infections. Patients undergoing hemodialysis (HD) treatment and kidney transplant recipients (KTR) are considered at risk of contracting fungal infections, but the few published data do not reach the conclusion of whether they are predisposed to OM. This study aimed to determine the prevalence and etiology of OM in these patients and to determine the antifungal susceptibility profile of the isolated fungal species. Methods: We recruited 149 HD patients, 187 KTR, and a control group comprising 174 patients attending an internal medicine service with other diseases than renal diseases. All patients underwent an examination of all toenails to check for the presence of OM. Antifungal susceptibility tests were performed following the Clinical and Laboratory Standards Institute (CLSI) recommendations. Results: The prevalence rates of OM in HD patients (23.4%) and KTR (23.0%) were significantly higher than those in age- and sex-matched control groups (13.2%). In HD patients, OM was associated with diabetes but not with the duration of dialysis. In KTR, OM was more prevalent in those without diabetes and likely also in those using mycophenolate mofetil or azathioprine but was not associated with the duration of transplantation. Trichophyton rubrum was the most prevalent species (45.9%) followed by T. mentagrophytes (24.5%) and Candida parapsilosis (18.0%). Fluconazole, itraconazole, voriconazole, and terbinafine were all efficient against the isolates of dermatophyte, with terbinafine showing the lowest and fluconazole the highest minimal inhibitory concentrations. All isolates of C. parapsilosis were sensitive to the antifungals according to the CLSI criteria. Conclusion: We found a high prevalence of OM in HD and KTR patients and suggest that these conditions should be considered a risk factor of OM. All 4 antifungals evaluated in the study showed good in vitro activity against the etiologic agents.