Objective: To determine the frequency of anterolateral ligament (ALL) injury in patients with acute anterior cruciate ligament (ACL) rupture and to analyse its associated injury patterns. Methods: Ninety patients with acute ACL rupture for which MRI was obtained within 8 weeks after the initial trauma were retrospectively identified. Two radiologists assessed the status of the ALL on MRI by consensus. The presence or absence of an ALL abnormality was compared with the existence of medial and lateral meniscal tears diagnosed during arthroscopy. Associated collateral ligament and osseous injuries were documented with MRI. Results: Forty-one of 90 knees (46 %) demonstrated ALL abnormalities on MRI. Of 49 knees with intact ALL, 15 (31 %) had a torn lateral meniscus as compared to 25 torn lateral menisci in 41 knees (61 %) with abnormal ALL (p = 0.008). Collateral ligament (p ≤ 0.05) and osseous injuries (p = 0.0037) were more frequent and severe in ALL-injured as compared with ALL-intact knees. Conclusion: ALL injuries are fairly common in patients with acute ACL rupture and are statistically significantly associated with lateral meniscal, collateral ligament and osseous injuries. Key Points: • ALL injuries are fairly common in patients with acute ACL rupture. • ALL injuries are highly associated with lateral meniscal and osseous injuries. • MRI assessment of ACL-injured knees should include evaluation of the ALL.