A study of 4,247 shockwave lithotripsy treatment was performed to identify and analyze the risk factors for the development of post-extracorporeal shock-wave lithotropsy hematomas. The Dornier HM-3 and HM-4 lithotriptors were used. We recognized 23 hematomas in 23 patients (0.54%). Various factors were examined to identify the certain predisposing risk factors. There was no correlation of sex, age, stone number, stone size, stone location, number of shock waves and voltage used with the occurrence rate of hematoma. We found that patients with pre-existing hypertension and especially those with poor control of it had a significantly increased incidence of perinephric hematoma.