In order to determine the influence of rheumatoid factor in serum specimens on the specificity of an immunochromatographic test for the detection of antibodies against dengue virus, 50 clinical specimens containing rheumatoid factor were evaluated for cross reactivity with a commercially available assay. While specificity for the detection of immunoglobulin (Ig) G antibodies was 100%, the IgM component of the test showed false-positive results in 26% of cases. Thus, it is important to consider interference by rheumatoid factor when using immunochromatographic assays for the detection of specific IgM produced during dengue infection.