Authors present an estimation of articulo-trochanteric-distance (ATD) and ATD index in patients with Perthes disease and if there is any correlation between ATD and ATD index and age at the onset, gender, type of treatment, Herring and Stulberg classification. The study population consisted of 242 patients (35 female and 207 male) who had reached skeletal maturity at last follow up. The mean age at the onset of symptoms was 7 years and 4 months. All patients were treated by containment methods (bed rest and traction in abduction, brace, Petri cast, varus osteotomy, Salter osteotomy and shelf operation). ATD was estimated according to the Edgren methods and ATD index was calculated as relation ATD on Perthes site to ATD in normal joint. The late results were classified according to the Stulberg classification. Statistical analysis did not revealed any correlation between the age at the onset, gender and ATD index and ATD during last follow up. Both parameters decreased with poor results according to the Stulberg classifications. ATD index and ATD were statistically significant less after surgical treatment than after non-operative treatment. The same relations were seen between patients with leg length discrepancy (LLD) and without LLD. Patients in Herring group A had statistically significant bigger both parameters than patients in group B, C and patients in Herring group B than C. Articulo-trochanteric-distance and ATD index decreased during follow up and ATD decreased also in normal joint. In our opinion ATD index is a more reliable radiological parameter than ATD. ATD index decreases with bigger necrosis of the femoral head and poor result according to the Stulberg classification. This parameter is an evidence of the dysfunction proximal femoral growth plate in patients with LLD. The most decreased ATD index was observed after surgical treatment. There was no correlation between the age at the onset, gender and ATD index at last follow up.