Background: The purpose of this case series was to retrospectively compare radiological, clinical and functional outcomes and complications of diagnostic arthroscopy with open Latarjet procedures pre- and postoperatively within one year after surgery. Additionally we compared the pathologic findings during diagnostic arthroscopy with the radiological findings in preoperative contrast enhanced CT or MRI scans. Methods: Between 07/2009 and 11/2013 46 cases with unidirectional antero-inferior shoulder instability were enrolled, 4 cases were lost during the follow-up within one year postoperatively. Plain radiographs, contrast enhanced multislice studies, Instability Severity Index, Constant, Duplay and Rowe Scores were obtained preoperatively. Diagnostic arthroscopy was performed in all cases prior to open Latarjet procedure. At one year follow-up Constant, Duplay and Rowe Scores were obtained; position and consolidation of the coracoid transfer were assessed by conventional x-ray studies. Results: At one year follow-up a significant improvement of all scores was recorded (Constant Score 95.8 vs. 86.7; Duplay Score 93.7 vs. 25.2, Rowe Score 98.1 vs. 31.7, (p < 0.001)). During arthroscopy 28 of 42 Hill-Sachs-lesions were considered as engaging. 8 HAGL (humeral avulsions of the gleno-humeral ligaments) and 4 IGHL (inferior gleno-humeral ligaments) lesions were detected of which none were suggested during the preoperative radiological investigation. Complications observed were: screw migration (5), hematoma (1), infection (1) and recurrence (1). Conclusion: The Latarjet procedure is a reliable technique with very good clinical outcomes. Diagnostic arthroscopy is a valuable tool to detect HAGL- and IGHL-lesions and to visualize the engaging potential of Hill-Sachs-lesions. An additional arthroscopy may help to indicate a Latarjet procedure and to address concomitant pathologies. Level of evidence: Level IV, case series.