Introduction Narrow band ultra violet-B (NBUVB) phototherapy is an effective and safe mode of therapy for chronic plaque psoriasis. However the degree of action has been shown to vary with various factors such as age, extent of the lesions, tolerance of NBUVB and duration of the illness Objective This study aimed at describing factors influencing the response to NBUVB among patients with chronic plaque psoriasis treated at the District General Hospital (DGH), Matara. Method A descriptive study

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... arried out at the Dermatology Unit, DGH, Matara, among a convenient sample of patients with chronic plaque psoriasis who received NBUVB during a period of one and half years. The response to NBUVB was calculated as the difference between the initial and the post treatment psoriasis area severity index (PASI) scores as a percentage of the initial score. Age, initial PASI score, cumulative dose, erythema response and disease duration were assessed for their influence on the response to NBUVB using multiple regression analysis. Results A total of 63 patients were included and 46% were between 41-60 years of age. The study results showed that 36(57%) patients had 75-89% (PASI-75) reduction in the post treatment PASI, indicating that they had 75-89% clearance of skin lesions following the NBUVB treatment. Age, initial PASI score, cumulative dose and maximum erythema response dose did not show a significant correlation with the response rate. Only the duration of the illness had a significant moderate correlation with response rate (standardized coefficient (beta) = -0 .476, p = 0.01). Conclusion Efficacy of the NBUVB therapy is high if the duration of the illness is shorter. Therefore, NBUVB needs to be considered as a treatment option early in the disease.