The goal of this study was to determine the prevalence of associated acetabular cartilage lesions and labral tears in patients with cam-type femoro-acetabular impingement (FAI). We evaluated acetabular cartilage lesions and labral tears found during hip arthroscopy in 52 patients with radiological signs of cam-type FAI. We found a high prevalence of associated lesions (86.5%) in patients with cam-type FAI. They were graded according to the morphology, extent, and location of the lesion. Forty-one patients (78.8%) had an acetabular cartilage lesion. Labral tears were found in 31 patients (59.6%). There was a high correlation between age and the presence and extent of acetabular cartilage and labral lesions (r = 0.70; p < 0.0001 and r = 0.45; p <0.001 respectively). There was also a high correlation between the extent of the acetabular cartilage lesion and the presence of labral lesions (r = 0.62; p < 0.0001). Despite the recognized consequences of associated lesions on treatment and outcome, no classification system includes this aspect of FAI. Based on our findings, we developed a system to grade acetabular cartilage lesions according to their morphology and extent. This information can help to define the natural history of cam-type FAI, and to determine appropriate treatment.