Seborrhoeic dermatitis usually starts at puberty with a peak incidence at 40 years of age and is more common in males. Patients develop symmetrical, well demarcated, dull or yellowish red patches and plaques with overlying adherent, yellowish greasy scales. Seborrhoeic dermatitis has a distinctive distribution in areas rich in sebaceous glands - the scalp, eyebrows, glabella, nasolabial and nasofacial folds, cheeks, peri-auricular skin, pre-sternal and interscapular areas. It may occur in flexures, especially the axillae, groin, anogenital skin, infra-mammary skin and the umbilicus. Some patients may develop blepharitis with erythematous eyelids and destruction of eyelash follicles. Patients with HIV infection, neurological diseases, including parkinsonism and cranial nerve palsies, have a higher incidence of seborrhoeic dermatitis. Patients presenting with sudden onset severe seborrhoeic dermatitis should be screened for risk factors for HIV. Patients should be referred in the following situations: diagnostic uncertainty - consider other differential diagnoses; failure to respond to first-line treatment after four weeks - consider secondary changes e.g. bacterial infection, flexural intertrigo, lichenification, otitis externa; and severe/widespread disease. Patients with seborrhoeic dermatitis have a good prognosis, particularly infantile seborrhoeic dermatitis, which usually remits within a few weeks or months and does not recur.