OBJECTIVE:: To make evidence-based recommendations concerning the evaluation of the child with microcephaly. METHODS:: Relevant literature was reviewed, abstracted, and classified. Recommendations were based on a 4-tiered scheme of evidence classification. RESULTS:: Microcephaly is an important neurologic sign but there is nonuniformity in its definition and evaluation. Microcephaly may result from any insult that disturbs early brain growth and can be seen in association with hundreds of genetic syndromes. Annually, approximately 25,000 infants in the United States will be diagnosed with microcephaly (head circumference <-2 SD). Few data are available to inform evidence-based recommendations regarding diagnostic testing. The yield of neuroimaging ranges from 43% to 80%. Genetic etiologies have been reported in 15.5% to 53.3%. The prevalence of metabolic disorders is unknown but is estimated to be 1%. Children with severe microcephaly (head circumference <-3 SD) are more likely (∼80%) to have imaging abnormalities and more severe developmental impairments than those with milder microcephaly (-2 to-3 SD; ∼40%). Coexistent conditions include epilepsy (∼40%), cerebral palsy (∼20%), mental retardation (∼50%), and ophthalmologic disorders (∼20% to ∼50%). RECOMMENDATIONS:: Neuroimaging may be considered useful in identifying structural causes in the evaluation of the child with microcephaly (Level C). Targeted and specific genetic testing may be considered in the evaluation of the child with microcephaly who has clinical or imaging abnormalities that suggest a specific diagnosis or who shows no evidence of an acquired or environmental etiology (Level C). Screening for coexistent conditions such as cerebral palsy, epilepsy, and sensory deficits may also be considered (Level C). Further study is needed regarding the yield of diagnostic testing in children with microcephaly.