Tinea cruris is a dermatophytosis caused by Tricophyton rubrum and Epidermophyton floccosum found on the skin of the thighs, genitals, buttocks, around the anus and perineum. The typical clinical symptoms of tinea cruris are itching that increases when sweating, with polycyclic/round lesions with firm boundaries, polymorphic efflorescence, and more active edges. The diagnosis is based on history taking and dermatologic physical examination. In this case the patient is an 18-year-old female, presenting with a chief complaint of reddish and scaly patches on the buttocks and thigh folds that are increasingly widespread accompanied by intense itching, especially when sweating. The patient's complaint has been experienced since 3 months ago. The patient's reddish lesions appeared central healing with firm boundaries and active lesion edges arranged in a polycyclic manner. The patient underwent KOH examination and the results were spores (+) and hyphae (-).The prognosis of tinea cruris will be good if treated properly, unless re-exposure to the causative fungus.