Radial head fractures, particularly Mason I and II, are considered "harmless" injuries, and their severity is underestimated. In recent years, associated injuries to ligaments, cartilage, and adjacent bones have been studied in more detail. This meta-analysis collects the data on their incidence from the current literature. A systematic review of the online databases PubMed, EMBASE, CINAHL and Cochrane Library was performed to identify clinical studies on associated injuries in radial head fracture. Their incidence was assessed as weighted means and broken down into Mason types. The clinical relevance of these injuries was not primarily assessed, but all available data were collected. Data on 1323 patients (48 % female) were extracted from 11 studies. 66 % had a Mason I, 21 % a Mason II, and 13 % a Mason III injury. In 33 % of all patients, associated injuries were found. The most common injury was damage to the lateral collateral ligaments (51 %), the second most common to the capitellum (22 %). 82 % of the Mason III fractures had associated injuries, compared to 36 % in Mason II, and 15 % in Mason I. Data on the clinical relevance of these injuries showed a rate of 11 % of persisting complaints requiring further treatment. Associated injuries with radial head fractures are more frequent, and need treatment more frequently, than commonly assumed. Even in "harmless" Mason I fractures, severe associated injuries requiring surgical treatment are frequent. For clinical practice, persisting pain, even in a "simple" Mason I injury, should lead to a timely, specialised assessment and treatment.