Background: 8-Oxoguanine is one of the major products of DNA oxidation. It is considered a key parameter in the mutagenic and carcinogenic effect of ultraviolet radiation in humans.Objective: To assess and compare the carcinogenic potential of different photo(chemo)therapeutic modalities (namely NBUVB, PUVA and BB-UVA) in a variety of skin diseases by measuring 8-oxoG level in dark-skinned individuals before and after photo(chemo)therapy.Patients and methods: A prospective, randomized controlled, pilot study was conducted on 63 patients with photoresponsive dermatoses, in the form of vitiligo, psoriasis, and mycosis fungoides. The patients had skin types III-V. The patients were divided into three groups; group 1 (received NB-UVB), group 2 (received PUVA) and group 3 (received BBUVA). Biopsies were taken from all patients before and after phototherapy and only one biopsy was taken from sun-exposed skin of each of the 21 controls. 8-OxoG was measured by ELISA before and after therapy.Results: Regardless of the disease, a significantly higher level of 8-oxoG level (P = 0.000) and a significant positive correlation were found between 8-oxoG level in patients before versus after treatment by NBUVB (P = 0.000, r = 0.833), PUVA (P = 0.000, r = 0.724) and UVA (P = 0.000, r = 0.803. This before versus after rise was still within the range detected in control cases. A weakly significant positive correlation was found between cumulative dose and 8-oxoG level following PUVA therapy (P = 0.038, r = 0.455). Comparing 8-oxoG levels between skin types III and IV in controls showed a significantly lower value of 8-oxoG in skin type IV (P = 0.003).Conclusion: Any form of photo(chemo)therapy is expected to be followed by a rise in the level of 8-oxoG, which is expected to be within its normal range. This raise our attention to taking all the possible precautions needed to decrease the cumulative doses. Type of disease has no impact on the carcinogenic potential of photo(chemo)therapy. The higher the cumulative dose of PUVA, the higher the 8-oxoG level and the higher the risk of DNA damage. Both skin types III and IV seem to be safe, indicating that dark skinned individuals have less carcinogenic potential than fair ones. Longer studies with higher cumulative doses are needed to either confirm or negate our findings.