The fragile X syndrome is a relatively common form of mental retardation that tends to affect boys more severely than girls. The syndrome is associated with a fragile site at q27 on the X chromosome and with physical features including large or prominent ears and macro-orchidism. Four boys had physical and cytogenetic features of the fragile X syndrome. However, the IQ scores of these patients extended into the normal range. All four patients demonstrated similar learning difficulties that included hyperactivity, visuomotor incoordination, language deficits, and academic delays in mathematics. The fragile X syndrome should be considered in the differential diagnosis of learning disabled children.