Osteoid osteoma is a relatively common benign skeletal tumor that usually affects the cortex of the long bone. Despite its common incidence, the diagnosis is often delayed and confused with other entities such as stress fracture, tuberculosis, osteomyelitis and intracortical abscess. Moreover, the diagnosis becomes more difficult when the osteoid osteoma develops in the intra-articular region. Several factors contribute to the difficulty of the diagnosis: First, osteoid osteoma is relatively rare compared to other causes of articular pain. Second, it presents non-specific clinical manifestation in the hip joint much like other intraarticular disorders. Third, plain radiographs sometimes do not represent the characteristic findings. Fourth, MR imaging reveals inconsistent signal intensities, especially in the early stage. Bone scan also lacks specificity for diagnosis. Recently, we experienced four cases of intra-articular osteoid osteoma of the hip joint and presented them with a review of the literatures.