Cause of death is a commonly-found fact on death records.
Familypedia has a Property:Death causes, which is used (inter alia) in the mini-biographies that head most person articles. To set "death causes" as a property rather than just a note, so as to get it showing in the mini-biography, you need to find its box just below the death date boxes on Form:Person (since the 2012 improvements) or just fill in "|death causes=" if using the alternative semi-manual method.
The automated mini-biography prefixes the death causes with "of"; so state just the disease or sickness or say something like "injuries in traffic accident".
See also Causes of death.