- X-ray (of)
- Xanthelasma (eyelid) (palpebrarum), H02.60
- Xanthelasmatosis (essential), E78.2
- Xanthinuria, hereditary, E79.8
- Xanthoastrocytoma
- Xanthofibroma
- Xanthogranuloma, D76.3
- Xanthoma (s), xanthomatosis (primary) (familial) (hereditary), E75.5
- Xanthosis, R23.8
- Xenophobia, F40.10
- Xeroderma
- Xerophthalmia (vitamin A deficiency), E50.7
- Xerosis
- Xerostomia, K11.7
- Xiphopagus, Q89.4
- XO syndrome, Q96.9
- XXXXY syndrome, Q98.1
- XXY syndrome, Q98.0