BACKGROUND: There is mixed evidence for whether psychosocial assessment following hospital presentation for self-harm reduces self-harm repetition. A possible reason is the differences in professional background of assessors (primarily psychiatrists and psychiatric nurses) due to variability in training and therapist style. METHODS: Using data from the Oxford Monitoring System for Self-harm, we analysed data on patients making their first emergency department (ED) presentation for self-harm between 2000 and 2014, followed-up until 2015. Using logistic regression, we estimated the probability of repeat self-harm within 12 months, comparing: (i) patients receiving psychosocial assessment versus none, adjusting for age, gender, self-harm method, past self-harm presentation, and general hospital admission; and (ii) patients assessed by a psychiatric nurse versus those assessed by a psychiatrist, adjusting for age, self-harm method, time and year of presentation. RESULTS: The 12,652 patients who had an index ED presentation for self-harm during the study period accounted for 24,450 presentations, in 17,303 (71%) of which a psychosocial assessment was conducted; in 9318 (54%) by a psychiatric nurse and in 7692 (45%) by a psychiatrist. We found a reduced probability of repeat self-harm presentation among patients receiving psychosocial assessment versus none (adjusted odds ratio [AOR] = 0.70; 95% CI = 0.65-0.75; p