Pyrimidone is the name given to either of two heterocyclic compounds with the formula C₄H₄N₂O: 2-pyrimidone and 4-pyrimidone. The compounds can also be called 2-hydroxypyrimidine or 4-hydroxypyrimidine respectively, based on a substituted pyrimidine, or 1,3-diazine, ring.

Derivatives of pyrimidone are the basis of many other biological molecules, including:

• Nucleobases, such as cytosine
• Barbiturates, such as metharbital

• 
  Cytosine
• 
  Metharbital

• Antiulcer drugs including temelastine, icotidine, donetidine, and lupitidine.