Abstract Purpose Developmental dysplasia of the hip (DDH) varies from mild instability of the hip to subluxation or total dislocation of the joint. Well-known risk factors of DDH include pre-natal breech position, female sex, positive family history, hip side, primiparity and the mode of delivery. Aim of the present study was to further evaluate known risk-factors of DDH, find associations with more severe dysplasia (characterized with Ortolani positivity) and find risk factors of failure of the Pavlik harness treatment. Material and methods All children with the diagnosis of DDH treated in Tampere University hospital in the years 1998–2018 were retrospectively identified for the study and the data was collected from the medical records. Teratological dislocations (n = 3) were excluded from the analysis. Total of 945 patients were included. Results Breech presentation was strongly associated with Ortolani positivity (p < 0.001). Breech presentation was not associated with ending up for spica casting and/or operative treatment (p = 0.291) despite the association with Ortolani positivity. Ortolani positivity (p = 0.002), positive family history (p = 0.013) and girl sex (p = 0.029) were associated with ending up for spica casting and/or operative treatment. Conclusion Breech presentation seems to increase the risk of Ortolani positive DDH. However, these infants are likely to recover with initially started Pavlik harness treatment, as it was not associated with elevated risk for undergoing more robust treatments. Positive family history and girl sex are associated with the most severe cases of developmental dysplasia of the hip, and it may predispose to the failure of the Pavlik harness treatment.