PURPOSE: To assess the effect of direct three-dimensional (3D) magnetic resonance (MR) venographic findings on diagnostic thinking and therapeutic decisions in patients with complex recurrent varicose vein anatomy who were being evaluated for surgical treatment. MATERIALS AND METHODS: The study was approved by the Institutional Review Board; informed consent was obtained from patients. MR venography was performed before surgery in 22 legs of 14 patients (seven women: mean age, 53 years; seven men: mean age, 59 years) thought to have recurrent varicose veins. Two radiologists assessed image quality and evaluated sites and sources of varicose veins on MR venograms. One vascular surgeon completed a questionnaire before and after MR venography and noted diagnosis and therapeutic decisions. Diagnoses at MR venography were compared with surgical results in 19 legs that underwent surgery. Differences between diagnosed and treated varicose veins per leg before and after MR venography were analyzed with logistic regression for survey data. kappa Values were calculated to illustrate interobserver agreement for grading image quality of venous segments and for diagnosing recurrent varicose veins. RESULTS: Mean graded image quality of the deep venous system and the recurrent varicose veins was good or excellent in 89% of segments. There was good agreement between readers regarding grading of image quality of venous segments (kappa = 0.80). After MR venography, diagnosis of the sites and sources of recurrent varicose veins changed in 17 of 22 legs of nine of 14 patients. In one of 14 patients, the preoperative diagnosis of recurrent varicose veins was withdrawn. A change in treatment plan occurred in 17 of 22 legs after MR venography. The number of diagnosed and treated sources of reflux increased significantly after MR venography. MR venographic diagnoses were confirmed at surgery in all 19 legs. CONCLUSION: MR venographic results have a substantial effect on diagnostic thinking and therapeutic decisions when recurrent lower-limb varicose veins are suspected.