The behavioral manifestations of autism, including reduced sociability (reduced tendency to seek social interaction), may be related to underdevelopment of the corpus callosum (CC). The BALB/cJ inbred mouse strain is a useful model system for testing the relationship between reduced sociability and CC underdevelopment. BALB/cJ mice show low levels of sociability, on average, but substantial intrastrain variability in sociability, as well as striking variability in CC development. This study tested the hypothesis that sociability is positively correlated with CC size within the BALB/cJ inbred strain. 30-day-old BALB/cJ and C57BL/6J mice were tested for sociability towards gonadectomized A/J stimulus mice in a social choice task. The size of the corpus callosum was measured histologically at the midsagittal plane. BALB/cJ mice showed a significant positive correlation between the tendency to sniff the stimulus mouse and size of the CC relative to brain weight. C57BL/6J mice showed consistently high levels of sociability and normal corpus callosum development. These results suggest that abnormal white matter structure is associated with deficits in sociability in BALB/cJ mice. Additional studies are warranted to elucidate the relationship between brain connectivity and sociability in this model system.