Hypothyroidism is associated with significant neurocognitive deficits that develop across the life span. This article discusses the patterns of cognitive deficits associated with congenital and adult-onset hypothyroidism. A review of the extant literature shows that the successful treatment of clinically evident thyroid gland hypofunction, resulting in a return to euthyroidism in both infants and adults, may be associated with only partial and typically inconsistent patterns of recovery of overall neurocognitive function. In addition to demonstrating different patterns of cognitive impairments, patients with congenital and acquired adult-onset hypothyroidism have variable responses to thyroid replacement therapy, which increases the risk of higher neurocognitive morbidity associated with congenital hypothyroidism. An evaluation of the commonly held view that hypothyroid dementia is an imminently reversible condition is only partially supported by the medical literature, which is fraught with methodological and conceptual shortcomings. I offer some recommendations for addressing the cognitive and behavioral management concerns of individuals with clinical hypothyroidism.