Rheumatic diseases are among the oldest diseases recognized. The classification of rheumatic diseases is sometimes difficult due to unknown aetiology and heterogeneity in their clinical presentation. Osteoarthritis (OA) and rheumatoid arthritis (RA) are the two most common rheumatic diseases, accounting for a large percentage of disability worldwide. The economic and social burden of these diseases is great. Their impact on both individuals and society results from a decreased quality of life, lost productivity and increased costs of health care. Without appropriate approaches to patient management and control of these diseases, this impact can be expected to increase as the population ages. One of the challenges in studying OA and RA, and rheumatic diseases in general, is deriving epidemiological data that can be used to understand better the factors that contribute to the initiation and progression of these diseases. Only with such an understanding can significant progress be made in the diagnosis, treatment and management of patients.