We present genotype-phenotype correlations in two patients with distal 10q deletion. A patient with a small terminal deletion presented mild mental retardation and behavioral difficulties with hyperactivity, whereas the patient with a larger deletion, had multiple congenital anomalies and moderate mental retardation. Our observation confirms the previous suggestion that larger deletions of distal chromosome 10q are associated with a more severe clinical presentation, whereas hyperactive behavior may be a specific feature of small terminal deletions of chromosome 10q26.