BACKGROUND: The association of cardiorenal syndrome (CRS) with mortality in children with dilated cardiomyopathy (DCM) is unknown. METHODS: With a modified Schwartz formula, we estimated glomerular filtration rates (eGFR) for children >/=1 year of age with DCM enrolled in the Pediatric Cardiomyopathy Registry at the time of DCM diagnosis and annually thereafter. CRS was defined as an eGFR of <90 mL/min/1.73 m(2). Children with and without CRS were compared on survival and serum creatinine concentrations (SCr). The association between eGFR and echocardiographic measures was assessed with linear mixed-effects regression models. RESULTS: Of 285 eligible children with DCM diagnosed at >/=1 year of age, 93 were evaluable. CRS was identified in 57 of these 93 children (61.3 %). Mean (standard deviation) eGFR was 62.0 (22.6) mL/min/1.73 m(2) for children with CRS and 108.0 (14.0) for those without (P < 0.001); median SCr concentrations were 0.9 and 0.5 mg/dL, respectively (P < 0.001). The mortality hazard ratio of children with CRS versus those with no CRS was 2.4 (95 % confidence interval 0.8-7.4). eGFR was positively correlated with measures of left ventricular function and negatively correlated with age. CONCLUSIONS: CRS in children newly diagnosed with DCM may be associated with higher 5-year mortality. Children with DCM, especially those with impaired left ventricular function, should be monitored for renal disease.