Very preterm (VPT) birth can account for thinning of the corpus callosum and poorer cognitive performance. Research findings about preterm and VPT adolescents usually describe a small posterior corpus callosum, although our research group has also found reductions of the anterior part, specifically the genu. The aim of the present study was to investigate the functional implications of this concrete reduction. Fifty-two VPT adolescents were compared with 52 adolescents born at term; there were no significant differences in age and gender, and socioeconomic status was similar between the groups. All participants underwent a magnetic resonance imaging (MRI) study and assessment of prefrontal functioning and vocabulary. The VPT group showed significant reductions of the genu, isthmus and splenium, as well as a significantly worse performance on category verbal fluency, executive functions, everyday memory and vocabulary. Although several parts of the corpus callosum correlated with some prefrontal functions, the genu was the part which principally explained these correlations. The subtest Vocabulary only correlated with the splenium. The relationship between genu and prefrontal functions and between splenium and vocabulary may be due to the fact that these parts of the corpus callosum connect prefrontal and posterior parietal cortex, respectively. The work presented here provides evidence of specific associations between reductions in the anterior corpus callosum (genu) and lower prefrontal functioning in VPT adolescents.