Phototherapy with PUVA or UVB has been used to treat a wide variety of diseases such as psoriasis, vitiligo, atopic dermatitis and mycosis fungoides, etc. The present study was performed to investigate the pattern of phototherapy in the phototherapy clinic of Yonsei Medical Center. One thousand six hundred ninety two patients who received PUVA or UVB phototherapy were included in this study. We analyzed the protocols for phototherapy between 1985 and 1994. The number of phototherapy per year increased sharply until 1991 and thereafter it has remained relatively constant. The most common age group at the start of phototherapy was the third decade. The most common indications for PUVA and UVB phototherapy were vitiligo and psoriasis, respectively. Most patients had received less than 50 treatments of PUVA and less than 200 J/cm² of cumulative UVA. Most patients had received less than 50 treatments with UVB and cumulative UVB doses were variable. We had not found any malignancy in the skin. Since the maximum safe cumulative doses of UVA or UVB have not yet been established, it is difficult to decide when phototherapy should b discontinued. The data presented in this study needs to be further analyzed in correlation with photoaging and cancer development for the safe usage of phototherapy.