Hone your clinical reasoning and diagnostic skills with a new series of case-based topic-specific studies. This compilation of twenty neurology-related cases includes presenting clinical manifestations and a discussion of the broad range of possible diagnoses, with a reveal of the actual diagnosis at the end. Does this child have a classic presentation of a rare condition or an atypical presentation of a common diagnosis? Does the patient have a primary neurological condition or a neurological manifestation of a systemic disease? Several patients in this collection presented with ataxia, but their final diagnoses range from the unsurprising cerebellar tumor to uncommon conditions like heavy metal poisoning and rare genetic disorders. Does the child with diffuse weakness have a classic condition such as Guillain-Barré syndrome, a vitamin deficiency, one of the periodic paralyses, or an autoimmune disorder such as myasthenia gravis? Cases also include relatively new conditions such as autoimmune encephalitis or genetic disorders but remind us not to overlook well-known but now uncommon conditions like vitamin deficiencies or remote neurological dysfunction due to cancer in another organ.