The aim of this single centre retrospective study was to assess the outcome of patients after the fixation of slipped upper femoral epiphysis (SUFE) using a single cannulated screw. Thirty-eight slips, 28 stable and 10 unstable were treated with single in-situ screw fixation. The minimum follow-up was 1 year. The overall adverse outcome in terms of avascular necrosis (AVN), chondrolysis and revision surgery for slip progression was 18%, which was considered satisfactory. Slip progression of more than 10° was higher in the unstable when compared with the stable group but not statistically significant. Two out of the nine satisfactorily fixed unstable slips required revision surgery as opposed to none in the stable group. The incidence of AVN in the unstable group was 20%. There were no cases of AVN in the stable group. The adverse outcome in terms of AVN, chondrolysis and revision surgery for slip progression was significantly higher in the unstable group. In our study, results of single screw fixation for SUFE were found to be satisfactory as shown by earlier studies with the unstable SUFEs as expected having a poorer outcome when compared with the stable SUFEs.