We studied the incidence of rubromycosis of large folds in outpatients, analyzed the characteristic features of the course, justified the criteria of the differential diagnosis of rubromycosis and epidermophytia of large folds, and assessed the efficacy of sertaconazole (Zalain). Material and methods. The work was carried out as the part of a multicenter study (2012—2013) conducted in 50 regions of the Russian Federation. Results. Rubromycosis of large folds is characterized by more aggressive course compared to epidermophytia. The process more often involves two or more large folds (1.6 times), including intergluteal fold (2.6 times). Foot and toenails are most commonly involved (1.6 and 2.7 times, respectively), often with multiple onychomycosis (2.8±0.4), which if mostly hypertrophic. There is also hand mycosis (20%) with onychomycosis (17.1%) and lesions at other areas of the skin (51.4%). Mycotic eczema is the most common complication (1.7 times). Sertaconazole (Zalain) is an effective drug to treat rubromycosis of large folds, particularly in combination with athlete’s foot, onychomycosis with SCIO index of 1—2, and involvement of other areas of the skin. Conclusions. The rate of resolution of clinical manifestations in patients with rubromycosis of large folds correlates with the age of patients (older then 35 years), disease duration (more than 2 months), the presence of concomitant somatic pathology, the number of folds involved in the process, the presence of athlete’s foot and onychomycosis, the presence of complications of the underlying disease (secondary pyoderma, mycotic eczema), and the history of using various topical antimycotics. These factors determine the contingent of patients who need the maximum period of treatment of 1 month.