Abstract Purpose The failure rate following posterolateral corner reconstruction (PLC) remains high. Previous research indicates that in posterior cruciate ligament (PCL) reconstruction the laxity is affected by the tibial slope (TS). However, there is currently no literature evaluating the impact of TS on surgical outcome in combined reconstruction of PLC/PCL. Methods This study analyzed 47 patients in a retrospective cohort study who underwent PCL and anatomical PLC reconstruction according to techniques described by Arciero or LaPrade. TS was measured, and patients were divided into two groups: Group A (n = 16) with TS < 8° and Group B (n = 31) with TS ≥ 8°. After a minimum follow-up of 12 months, the side-to-side difference (SSD) of posterior tibial translation (PTT) was assessed using instrumented stability testing (Rolimeter), and various patient-reported outcome measures (IKDC, Lysholm) were collected and compared. Results At a mean follow-up of 17.7 ± 4.7 months, group A exhibited a higher SSD of PTT (A 3.9 mm ± 2.1 vs. B: 2.8 mm ± 1.5; p < 0.05). A negative correlation was observed between SSD of PTT and both TS (r = − 0.43; R 2 = 0.18; p < 0.01) and the Lysholm Score (r = − 0.41; R 2 = 0.17; p < 0.01) in the overall cohort. Subgroup analysis revealed a higher Lysholm Score in patients with a postoperative SSD of PTT less than 4 mm (85.7 ± 10.1 vs. 79.2 ± 6.6; p = 0.0006). Conclusion In combined PCL and anatomic PLC reconstruction a TS < 8° results in elevated SSD of PTT. A flattened TS is linked to higher remaining SSD of PTT, while lower SSD of PTT is associated with improved clinical outcomes. Level of evidence Retrospective Cohort Study, IV.