Introduction: The management of testicular cancer (TC) requires a complex multimodal therapeutic approach. Despite the availability of regularly updated guidelines, non-guideline-concordant treatment of TC still occurs. The purpose of the present study was to evaluate the compliance patterns in diagnosis and therapy and their potential effects on patient outcomes with respect to the guidelines of the European Association of Urology., Patients and Methods: We performed a retrospective analysis of 131 patients diagnosed with TC who had been referred to our department from September 2015 to October 2016. Patient characteristics were compared with European Association of Urology guideline recommendations., Results: Of the 131 primary treated patients, 23 (18%) had received a non-guideline-concordant treatment. The most common error was undertreatment (n = 12; 52%), mainly due to missing chemotherapy cycles. Overtreatment occurred in 30% of patients (n = 7); however, inappropriate treatment (n = 2; 9%) and misdiagnosis (n = 2; 9%) were rarely observed. In salvage therapy, non-guideline concordant treatment was observed less frequently compared to patients receiving primary therapy (12% vs. 18%). Of the 131 patients, 35 developed a relapse, 23 of whom were treated correctly and 6 of whom were undertreated. Undertreatment of patients resulted in significantly reduced relapse-free survival compared with guideline-concordant management in primary treated patients (P = .005)., Conclusion: Despite the standardization of treatment by interdisciplinary guidelines, its integration into daily practice remains limited. Undertreatment of TC patients is associated with significantly reduced relapse-free survival and should thus be avoided., (Copyright © 2017 Elsevier Inc. All rights reserved.)