In recent decades, the understanding of the cerebellum has advanced far beyond considering it an organ of motor function alone. Emotional, behavioral, and cognitive functions of the cerebellum are now well-documented, and a broad range of injuries have been reported to result in cerebellar cognitive and affective syndrome (CCAS). Even with these recent advances, there remains a vast expanse to explore and understand about this fascinating region of the human brain, particularly in terms of pediatric manifestations, CCAS in the setting of neurodevelopmental disabilities (NDD), and neuropsychiatric and behavioral interventions for individuals with CCAS. Here we describe two pediatric cases that illustrate the importance of CCAS in pediatric neuropsychiatry: one with a history of a stable posterior fossa tumor, and the other with congenital changes to the cerebellum due to a rare neurodevelopmental syndrome. Both individuals developed a complex array of neuropsychiatric symptoms at a young age, including symptoms suggestive of bipolar affective disorder, both of whom responded to lithium. This chapter discusses the diagnosis and implications of CCAS and the posterior fossa in pediatric neuropsychiatry, including a growing understanding of the heterogeneity of the etiologies, manifestations, courses, and outcomes of CCAS.