Three developmental screening tests (the Denver-II, Battelle Developmental Inventory Screening Test, and Early Language Milestone Scale-2) were administered to 18 infants and toddlers (13 boys and 5 girls) with confirmed diagnoses of fragile X syndrome as part of a comprehensive developmental assessment at 9, 12, and 18 months of age. The Denver-II identified delays for 10 of 11 boys at 9 months of age and the Denver-II and the Early Language Milestone Scale-2 identified delays in 100% of the boys at 12 and 18 months. The Battelle Developmental Inventory Screening Test identified delays in 75% of the children at 12 and 18 months. When compared with more comprehensive developmental tests (Mullen Scales of Early Learning and Receptive-Expressive Emergent Language Scale-2), the screening tests concurred at least 76% of the time at the 12- and 18-month assessments. These results indicate that developmental delays could be detected in most children with fragile X syndrome through routine developmental screening by the age of 9 to 12 months.