Patients whose symptoms include widespread, diffuse musculoskeletal pain are commonly referred for rheumatological evaluation, even when the underlying cause may lie out with the remit of rheumatology. A diagnosis of fibromyalgia may seem highly probable even from the referral letter, or after a few leading questions during the consultation. However, the lack of specificity of the many symptoms associated with widespread pain means that other diagnoses have to be considered. The history and examination must bear in mind alternative and concomitant musculoskeletal disorders, such as mild systemic lupus erythematosus, polyarticular osteoarthritis, rheumatoid arthritis, polymyalgia rheumatica, hypermobility syndromes and even osteomalacia. Non-rheumatological diseases may also have symptomatic similarities to fibromyalgia, including neoplastic and neurological diseases, hypothyroidism and other endocrine disorders, chronic infections, as well as a variety of psychiatric conditions. A rational approach to investigation will usually allow other diagnostic possibilities to be excluded without reinforcing the abnormal illness behaviour so common in chronic pain states.