Partial monosomy of distal 10q is an uncommon chromosomal disorder. Its characteristic features include growth retardation, psychomotor delay, facial dysmorphia, congenital heart disease, and anogenital/urinary tract anomalies. Reported here is a female infant at age 4 months who was diagnosed with a de novo deletion of the long arm of chromosome 10, with a breakpoint at 10q26. Using the Bayley scales of infant development II, she was found to have mild psychomotor delay. We also review the related literature of partial deletion of the long arm of chromosome 10.