Knowledge of filariasis and perceptions of the disease were explored among 413 lymphoedema cases attending two filariasis clinics in the Colombo district of Sri Lanka. The information was collected in interviews based on a pre-tested, interviewer-administered questionnaire. Only 15% of the patients had initially attributed their limb swelling to filariasis. Most knew that filariasis resulted from mosquito bites (81.1%) and that the disease is transmissible (59.8%) and preventable (74.3%). The majority did not know, or were uncertain, whether filariasis causes swelling of the breasts in females (68.5%), scrotal swelling (60.7%) or dry cough/breathlessness (62.7%). Most (60%) of the interviewees wrongly believed that chronic filarial lymphoedema could be cured, primarily by long-term treatment with diethylcarbamazine. Knowledge of filariasis was significantly associated with level of education (P<0.05). Curiously, compared with the male interviewees, the females interviewed were much less likely to say that filariasis was the cause of their initial swelling (P<0.001). Those who had suffered with the disease for more than 1 year were not significantly more knowledgeable about the disease than the interviewees who had developed symptomatic filariasis more recently. Knowledge about the symptoms of filariasis was generally poor in the study population. In order to dispel several common myths about the disease, health-education programmes, that are targeted both at the community in general and at primary-care providers, are clearly needed.