Duration of untreated psychosis (DUP) is considered an important factor in outcome. Individual, familial and illness factors may prolong DUP. Little data on this issue is available from the country of Nepal. The purpose of the present study was to assess DUP in patients with first-episode psychosis and identify associations with patients' socio-demographic and clinical factors. A cross-sectional, descriptive study was conducted in the department of psychiatry, of Tertiary Hospital in the Eastern part of Nepal. Eighty-six patients were enrolled. ICD-10 was used to make the diagnosis. Nottingham Onset Schedule-DUP version (NOS-DUP) was used to assess DUP. Positive and Negative Syndrome Scale (PANSS) was used to assess patients' clinical symptoms. The mean (SD) DUP was 21.4 (42.1) months and median DUP was 3.0 months (IQR = 23.5). Participants from mountainous region, the unemployed, having an insidious onset of illness, and patients with a diagnosis of schizophrenia had significantly longer DUP (P < .005). Duration of untreated psychosis was also positively correlated with negative symptoms (r = .42, (P < .001) and total PANSS score (r = .42, P < .001). Duration of untreated psychosis in first-episode psychotic patients was relatively long (compared to studies in other countries), and was found to be positively associated with mountainous regions of Nepal, being unemployed, having an insidious onset of illness, and having a diagnosis of schizophrenia. Programs and educational efforts are needed to ensure early treatment of patients with first-episode psychosis, especially in the mountainous rural areas of Nepal.