We have compared the findings of MRI with those of hip arthroscopy in 23 hips in young adults with hip pain. Large deep cartilage deficiencies on the acetabulum or femoral head, the percentage of femoral head cover, and the presence of marginal osteophytes seen on MRI correlated well with those seen at arthroscopy, but chondral softening, fibrillation, or partial-thickness defects less than 1 cm in diameter were less consistently detected by MRI. Osteochondral loose bodies and labral tears were not well demonstrated by MRI, but were readily identified and treated at arthroscopy. Arthroscopy of the hip is a useful investigation for hip pain in young adults especially when standard non-invasive MRI fails to provide a clear diagnosis.