BACKGROUND In lymphatic filariasis due to Wuchereria bancrofti infections, the relationship between the natural course of infection and development of clinical disease remains controversial. The two hypotheses that are widely considered are (1) microfilaraemia represents an early stage of infection which progresses to amicrofilaraemic clinical disease and (2) microfilaraemia and clinical disease are two sequentially unrelated independent entities of the filarial infection and disease. Aim To determine whether microfilaraemic individuals develop lymphatic disease. METHODS The study was conducted in Sri Lanka during the period 1982 to 1998. There were two components, firstly a cross-sectional study and then a longitudinal study. Microfilaraemia was determined by microscopic examination of night blood films. Microfilaraemia associated anti-filarial antibodies were determined by ELISA. Clinical examinations were performed to determine if the test subjects had evidence of acute and chronic lymphoedema. RESULTS Two major observations were made. First, the incidence and development of adenolymphangitis and lymphoedema in microfilaraemic individuals were very rare and these subjects maintained asymptomatic microfilaraemic status for very long periods of time. Second, in contrast to microfilaraemic subjects, the incidence and development of lymphangitis and lymphoedema were significantly higher in amicrofilaraemic anti-filarial antibody-positive subjects. CONCLUSIONS Microfilaraemia does not represent a precondition to development of clinical disease (except male genital involvement).