Dr Riordan undertook training in rheumatology in Australia and Oxford. He won the Michael Mason award to study crystal arthropathies in Bristol, UK. During his more than twenty-five years as a consultant rheumatologist in Wollongong, he has developed expertise in most areas of clinical rheumatology, especially inflammatory joint disease and connective tissue diseases. Dr Riordan has retained a specific interest in crystal arthropathies whilst developing extensive experience in giant cell arteritis (temporal arteritis), and large vessel vasculitis in addition to osteoporosis. He undertakes teaching of general medicine and rheumatology to medical students, interns, physician trainees, and advanced trainees in rheumatology (for the Royal Australian College of Physicians). Dr Riordan is head of the Department of Rheumatology at Wollongong Hospital, convener of the Australian Rheumatology Review Group (ARRG) (recent publications regarding vaccinations and anti-rheumatic drugs in cancer patients) and is a key member of the Friday Rheumatology Review Group.