Hypoplasia is an incomplete or arrested development of an organ or a part [1]. It is descriptive of many medical conditions such as:

• Underdeveloped breasts during puberty.
• Underdeveloped testes in Klinefelter's syndrome.
• Underdeveloped thymus in DiGeorge syndrome.
• Underdeveloped labia majora in popliteal pterygium syndrome.
• Underdeveloped cerebellum caused by mutation in the Reelin gene.
• Underdeveloped tooth caused by oral pathology, such as Turner's hypoplasia.
• Underdeveloped chambers of the heart in hypoplastic left heart syndrome and hypoplastic right heart syndrome
• Underdeveloped optic nerve in optic nerve hypoplasia
• Underdeveloped sacrum in sacral agenesis
• Underdeveloped facial muscle in asymmetric crying facies
• Underdeveloped thumb from birth.

See aplasia, atrophy.