This investigation was undertaken to establish more accurately the clinical features of the desease as seen in Korea, and to investigate susceptibility factors and to study the ecology of P. orbiculare in this condition. All of 50 new patients with Tinea versicolor attending the Ewha University Hospital, during a period of 6 months were studied personally. 1. Clinical feature: The sex ratio of the whole series was 32 males to 18 females. Twenty of 50 patients (40%) were between the age of 20 to 29 years. The duration of disease was more than 4 months in 37 of 50 patients (74%). The cases of first onset in June, July and August were 33 of 50 patients (66%). Whereas, the developed in December, January and February were only 3 of 50 patients (6%). Seasonal fluctuation was remarkable in 16 of 25 patients (66.7%) who had the duration of more than 1 year. The course of disease was rapid in 33 of 50 patients (66%) and slow in 9 of 50 patients (18%). Thirty-three of 50 patients (66%) had not any subjective symptoms. Thirteen patients (26%) had mild itching sensation and 4 patients (8%) had severe itching. The frequency of the first affected were neck (27.4%), axilla (19.2%) anterior chest (15.0%) and groin (11.0%). 7) Hyperpigmented lesions were observed in 35 of 50 patients (70%) and hypopigmented lesions were observed in 11 of 50 patients (22%). Skin lesions were noticed mainly in the anterior chest, neck, back and axilla, and more severe in the anterior chest, back and abdomen than other areas. Tinea versicolor was particularly prevalent in those persons who had occupations of mental work and who perspired every day or every 2 or 3 days. A positive family history of Tinea versicolor was obtained in 7 of 50 patients (14%). Fourteen of 50 patients (28%) had association with superficial fungal infections. 2. Mycological features: Typical appearance of M. furfur was observed in all scrapings from 25 lesions and only 3 scrapings from 20 clinically skin of the patients. P. orbiculare was seen on direct examination of scrapings from 24 of 25 skin lesions, from 19 of 20. clinically normal skin of patients and from 18 of 29 control normal skin. The quantity of P. orbiculare was greater in skin lesions and clinically normal skin area than in control normal skin surfaces.