Subtelomeric deletions have been reported in ∼2.5% of individuals with developmental disabilities. Subtelomeric deletion 2q37 has been detected in many individuals diagnosed with intellectual disabilities (ID) and autism spectrum disorders (ASD). Previously, genotype–phenotype correspondences were examined for their relationship to breakpoints 37.1, 37.2, or 37.3. Our purpose was to ascertain whether there were phenotypic differences at these breakpoints, elucidate the cognitive-behavioral phenotype in del2q37, and examine the genotype–phenotype association in the deletion with respect to cognitive-behavioral profiles and ASD. We administered a comprehensive cognitive-behavioral battery to nine children diagnosed with del 2q37, ages 3.9–17.75 years. ID for five tested with the Stanford–Binet (4th Edition) (SBFE) ranged from severe to mild [IQ Range: 36–59]. Adaptive behavior scores from the Vineland Adaptive Behavior Scale (VABS) were much below adequate levels (DQ Range: floor value [“19”] to 55). Autism scores from the Child Autism Rating Scale (CARS) ranged from 22 [non-autistic] to 56 [extremely autistic]; 5/8 [63%] children received scores on the autism spectrum. Participants with the largest deletions, 10.1 and 9.5 Mb, attained the highest IQ and DQ scores while those with the smallest deletions, 7.9 and 6.6 Mb, made the lowest IQ and DQ scores. No association between deletion breakpoint and phenotype were found. Assessment of the various deleted regions suggested histone deacetylase 4 gene(HDAC4)was a likely candidate gene for ASD in our sample. However, two earlier reports found no association betweenHDAC4haploinsufficiency and ASD. © 2016 Wiley Periodicals, Inc.