Potential risk factors for lymphatic filariasis (LF), including the failure to use insecticide-treated bednets (ITN), were studied in four north-eastern provinces of Cambodia, using 43 cases of LF and 248 apparently healthy controls who were matched with the cases in terms of age (+/-5 years), gender and village. The results of a univariate matched analysis indicated that lack of ITN [odds ratio (OR)=20.1; 95% confidence interval (CI)=2.2-182.4; P=0.008] and frequent overnight stays in forests or paddy fields outside the village (OR=3.6; CI=1.3-10.0; P=0.012) were the most important risk factors. In a multivariate matched analysis, frequent overnight stays outside the village combined with bednet use showed a clear dose-response relationship, with untreated nets offering significant protection during such stays but ITN offering significantly better protection. Even if villagers used ITN during such stays, they were significantly more likely to develop LF than villagers who did not travel (OR=5.0; CI=1.5-16.3; P=0.008), and if they used untreated or no nets while away they were even more likely than the non-travellers to develop the disease (OR=1413; CI=28.0-71,189; P<0.001). Taken together, these results provide further evidence for the importance of bednet use and their impregnation in the prevention of LF. At least in north-eastern Cambodia, the use of bednets and, preferably, ITN is particularly important during overnight stays outside the home village. In areas where LF is endemic, the sustained distribution of insecticide-treated bednets or hammock nets appears to be a very good idea.