To achieve symmetry in unilateral free flap breast reconstruction often requires a contralateral procedure. There is no evidence in the literature to support the benefit of immediate contralateral breast symmetrisation concomitant to breast reconstruction. We hypothesized that performing a simultaneous contralateral balancing operation at the time as the initial reconstruction might provide immediate symmetry and minimize the frequency of secondary procedures. Thus, we performed a comparative study on this issue. A comparative retrospective study was conducted on 78 consecutive patients who underwent unilateral breast reconstruction surgery with latissimus dorsi (LD) flap and contralateral breast symmetrisation from January 2014 to June 2016 at Turku University Hospital. Exclusion criteria included other breast reconstruction techniques and no contralateral symmetrisation at follow-up. The patients were divided according to the timing of contralateral breast balancing operation into an immediate versus a delayed group. Postoperative complications, outcomes, and re-operations were compared. Baseline characteristics were well balanced between the groups except for comorbidity, which was significantly higher in the immediate group. Mastectomy weights (735.6 vs. 390.7 g, p = 0.015), contralateral breast reduction weights (268.3 vs. 105.8 g, p = 0.014), and implant size (218.9 vs. 138.9 g, p = 0.001) were significantly larger in the immediate group. No significant differences in any kind of complications were detected. Similarly, the rates of re-operations were similar among the groups (24.0 vs. 43.3%, p = 0.134). Performing immediate symmetrisation at the time of breast reconstruction is safe and feasible in autologous LD breast reconstructions, where 76% did not require a second operation for symmetry. There were no differences in the rate of any re-operation and, therefore, performance of simultaneous contralateral reduction is a reasonable option.