The ability for mental calculation represents a fundamental prerequisite for development of intelligence, which is predictive for educational and professional success in life. Many individuals with calculation difficulties are survivors of premature birth. The brain mechanisms of these deficits are, however, largely unknown. In this work, we clarify whether and, if so, how calculation abilities in adolescents who were born premature are related to the extent and topography of periventricular lesions that affect brain connectivity. Performance on a set of mental calculation tasks is lower in adolescents with periventricular leukomalacia (PVL) than in former preterms and term-born peers without signs of brain abnormalities on a magnetic resonance imaging scan. No difference in the calculation ability was found between term-born and preterm adolescents without PVL. Calculation abilities in PVL patients were unrelated to volumetric extent and topography of lesions in both brain hemispheres. Whereas previous work clearly reveals the link between the extent and topography of lesions and severity of impairments in visual cognition ranging from body motion processing to visual navigation and social cognition, no such association occurs for mental calculation. We assume that the lack of relationship between calculation abilities and the extent and topography of periventricular lesions point to topographically restricted neural substrate that serves as the keystone for mental calculation. The findings suggest that periventricular brain damage does not substantially affect the connectivity of this region with other brain structures engaged in the mental calculation network. (Contains 5 figures and 1 table.)