The totality of effects of a particular drug on patients cannot be truly assessed until many patients have taken it. In order to assess the side effects of any drug, many thousands of patients may have to be observed, and the observation may have to extend over decades. Quinacrine hydrochloride (quinacrine) was used as a malarial-suppressive drug by allied soldiers during World War II. The most commonly occurring side effect was a drug eruption. This at times led to permanent sequelae at an early stage. Further observation revealed late sequelae occurring 7 to 17 years after the war. Two of these late sequelae were observed to become malignant, and in most cases the palmar aspect was involved. This is an area which rarely shows malignant change. It has been observed that quinacrine can be instrumental in inducing skin cancers as late as 34 years after its ingestion.