Damage to the prefrontal cortex in childhood can produce long-term impairments of emotion, behavior regulation, and executive functions, but little is known regarding the earliest expression of these impairments. We describe here detailed behavioral studies of a boy at 14 months of age (‘PF1’) who sustained focal damage in the right inferior dorsolateral prefrontal cortex due to resection of a vascular malformation on day 3 of life. The surgery was followed by a good medical recovery, and he reached developmental milestones at a normal rate. His neurological examination was normal, as were his mother's ratings of communication abilities, daily living skills, socialization, and motor skills. Multiple standardized laboratory paradigms were used to evaluate his behavior in structured and relatively unstructured situations designed to elicit positive and negative emotions and to place demands on attention. Relative to a comparison group of 50 age-matched boys with no neurological history, PF1 demonstrated significant impairments in the regulation of emotion and engagement of attention, particularly in unstructured conditions. These findings indicate that damage to prefrontal cortex in infancy begins to impact on emotional and cognitive development already during the first months of life.