Background Rhabdoid tumors are a rare and aggressive cancer subtype which is usually diagnosed in early childhood. Little is known about their etiology. The purpose of this study was to describe the epidemiology of rhabdoid tumors and examine their relation to perinatal characteristics. Methods We identified 44 atypical teratoid/rhabdoid tumors (AT/RT) of the central nervous system (CNS) and 61 rhabdoid sarcomas (renal and extra‐renal non‐CNS tumors) from California Cancer Registry records of diagnoses 1988–2007 among children <6 years of age. We randomly selected 208,178 controls from California birthrolls. Multivariable logistic regression was used to examine associations between rhabdoid tumors and perinatal characteristics. Results After adjustment for demographic characteristics, low birthweight (<2,500 g) strongly increased risk for developing both rhabdoid sarcomas (OR = 2.43, 95% CI 1.09, 5.41) and AT/RT (OR = 2.99, 95% CI 1.31, 6.84). Both preterm delivery (<37 weeks gestation, OR = 2.63, 95% CI 1.34, 5.17) and late term delivery (>42 weeks, OR = 3.66, 95% CI 1.54, 8.71) also increased risk of rhabdoid sarcomas. Rhabdoid sarcoma cases (OR = 3.08, 95% CI 1.11, 8.55) and AT/RT cases (OR = 3.16, 95% CI 1.23, 8.13) also were more likely to be multiple births. Conclusion The excess of twin pregnancies may suggest an association with infertility treatments. This is the first population‐based epidemiologic study to examine these rare tumors. Pediatr Blood Cancer 2013; 60: 77–81. © 2012 Wiley Periodicals, Inc.