Patched1 heterozygous knockout mice (Ptc1+/-), an animal model of multiorgan tumorigenesis in which ionizing radiation dramatically accelerates tumor development, were used to study the potential tumorigenic effects of electromagnetic fields (EMFs) on neonatal mice. Two hundred Ptc1+/- mice and their wild-type siblings were enrolled in this study. Newborn mice were exposed to 900 MHz radiofrequency radiation (average SAR: 0.4 W/kg for 5 days, 0.5 h twice a day) or were sham exposed. We found that RF EMFs simulating the Global System for Mobile Communications (GSM) did not affect the survival of the mice, because no statistically significant differences in survival were found between exposed and sham-exposed animals. Also, no effects attributable to radiofrequency radiation were observed on the incidence and histology of Ptc1-associated cerebellar tumors. Moreover, the skin phenotype was analyzed to look for proliferative effects of RF EMFs on the epidermal basal layer and for acceleration of preneoplastic lesions typical of the basal cell carcinoma phenotype of this model. We found no evidence of proliferative or promotional effects in the skin from neonatal exposure to radiofrequency radiation. Furthermore, no difference in Ptc1-associated rhabdomyosarcomas was detected between sham-exposed and exposed mice. Thus, under the experimental conditions tested, there was no evidence of life shortening or tumorigenic effects of neonatal exposure to GSM RF radiation in a highly tumor-susceptible mouse model.