Differential scanning calorimetry analyses of two easily prepared polymorphs of acetaminophen (also known as paracetamol) are recorded. The density of the forms can be found in the literature. Rules for heats of transition, heats of fusion, and density, as well as methods for determining the solid-solid transition temperature between the forms, are used to determine whether the two forms are enantiotropic or monotropic and to determine which is the more stable form at room temperature and pressure. (Contains 1 figure.)