After training in general practice and working as a family physician in Eastern Canada, Dr Greenstone did a residency in pediatrics and started consultation pediatrics in Surrey in 1977. He returned to family medicine in 2002.
Dr Greenstone has a keen interest in history in general, and enjoys studying medical history to compare trends in medical thinking and observe the progress of new ideas in medical theory and practice. Dr Greenstone's historical articles often delve into the histories of lesser-known figures and uncover their significant contributions to medical science.