XL (extra large)

XLA (X-linked agammaglobulinemia)

XLAS (X-linked Alport syndrome)

XLD (X-linked dominant)

XLMR (X-linked mental retardation)

XLR (X-linked recessive)

XML (extensible markup language)

XP (xeroderma pigmentosum)

XR (extended-release)

XR (x-ray)