Controversy remains as to whether the contralateral hip should be fixed in patients presenting with unilateral slipped capital femoral epiphysis (SCFE). This study compares the outcomes of those patients who had prophylactic fixation with those who did not. We identified 90 consecutive patients with a mean age of 12.3 years presenting to the study centre with SCFE from a prospective operative database. The patient's notes and radiographs were retrospectively analysed for post-operative complications, re-presentation with a contralateral slip, and the presence of a cam lesion. The mean length of follow-up was 8 years (range 3 to 13). Fifty patients (56%) underwent unilateral fixation and 40 patients underwent bilateral fixation, of which 4 (4%) patients had simultaneous bilateral SCFE and 36 (40%) had prophylactic fixation of the contralateral hip. Twenty-three patients (46%) that underwent unilateral fixation, went onto have contralateral fixation for a further SCFE. Two patients from this group had symptomatic femoracetabular impingement from cam lesions and one patient required a Southwick osteotomy for a severe slip. Five patients (10%) that had unilateral fixation only demonstrated cam lesions on radiographic analysis, being suggestive of an asymptomatic slip. No post-operative complications were observed for the contralateral hip in patients that had prophylactic screw fixation and no cam lesions were identified on radiographic assessment. This study suggests that the contralateral hip in patients presenting with unilateral SCFE should be routinely offered prophylactic fixation to avoid a further slip, which may be severe, and the morbidity associated with a secondary cam lesion