OBJECTIVEThe risk of hematoma formation in stereotactic procedures is generally considered to range between 1 and 4%, and it has been speculated that morphological procedures may have a higher risk of bleeding than functional procedures.METHODSBetween 1989 and 1999, all patients who underwent a stereotactic procedure performed by the same surgeon were enrolled sequentially onto the study. All patients had normal preoperative prothrombin time, partial thromboplastin time, and platelet count. High-resolution computed tomography or magnetic resonance imaging with a 1.5-T machine were used for the target definition. None of the patients had an angiogram before surgery.RESULTSA total of 361 procedures was performed comprising 175 morphological procedures (139 biopsies, 18 lesion evacuations [cysts, abscesses, and hematomas], and 18 drain implantations) and 186 functional procedures (137 lesions [thalamotomy or pallidotomy], 47 deep brain electrode implantations, and two physiological explorations without lesions or implantations). There were no infections or seizures in either group. Three hematomas (1.7%) occurred in the morphological group, two of them in inflammatory lesions in immunocompromised patients (one death) and one in a pineal tumor. Three hematomas (1.6%) occurred in the functional group (no mortality). There was no statistically significant difference (P> 0.05; Fisher’s exact test) in the risk of hematoma formation between morphological and functional stereotactic procedures. The morbidity and mortality related to bleeding also were not statistically different (P> 0.05; Fisher’s exact test) between these two groups.CONCLUSIONIn this series, the risk of bleeding was not higher for morphological procedures than for functional procedures. This suggests that the risk of bleeding for stereotactic procedures is related more to the patient than to the type of procedure performed. Our study confirms an overall risk of bleeding of 1.7% for any type of stereotactic procedure, resulting in a mortality of 0.3% and a morbidity of 1.4%.