In this study treatment results in children and adolescents (n = 32) suffering from loco-regional abdominal relapses of germ cell tumors (GCT) (7 embryonal carcinoma, 17 Yolk sac tumors, 8 immature teratomas) aged from 1;0 to 23;3 years (mean = 10;11 years) were evaluated. In this pilot study 9 patients were treated with cisplatinum (40 mg/m2 on days 1 and 4), etoposide (100 mg/m2 on days 1 to 4), and ifosfamide (2000 mg/m2 on days 1 to 4) (PEI) +/- radiation in combination with regional deep hyperthermia (RHI). In sedation RHT was induced by non-invasive heat applicators (Sigma-40 and Sigma 60, BSD Medical Corporation, Utah, USA). In 7 out of these 9 patients with recurrent GCT a tumor response (5 CR, 2 PR, 1 SD, 1 PD) was found. In addition, in 2 patients a complete tumor resection could be achieved inspite of 2 previous incomplete tumor resections each. Five out of 9 patients are living event-free after an observation period ranging from 8 to 40 months (median = 15 months). Treatment results of this RHT study population were compared with treatment results in patients with recurrent GCT, who received conventional relapse therapy (chemotherapy/ surgery +/- radiation) alone. In this matched cohort 5 out of 23 patients are living event-free after an observation time ranging from 1 to 120 months (median = 8 months). According to Kaplan-Maier life table analysis, patients with relapse therapy combined with RHT have an event-free survival (EFS) of 0.41 +/- 0.33 whereas the matched cohort without RHT have an EFS of 0.16 +/- 0.25. The difference in treatment results of both groups is significant (Wilcoxon/p = 0.03). From the data presented in this study we conclude that children with loco-regional recurrences of extracranial non-testicular GCT have an unfavorable prognosis, unless local tumor control can be achieved. The additional application of RHT in combination with conventional therapy (PEI chemotherapy +/- radiation) can improve local tumor control and EFS in GCT patients with loco-regional recurrences. Therefore, based upon these results in the future MAKEI trial RHT will be applied to GCT patients with poor response to neoadjuvant chemotherapy alone as first line treatment.