A 30-year-old woman with severe dengue presented on the sixth day of her illness with life-threatening thrombocytopenia, refractory to multiple platelet transfusions. Dengue IgM antibody and the non-structural-1 antigen tests as of day 3 were negative. The IgG antibody against the same was positive, suggesting a past episode of dengue. Since she had a history of menorrhagia prior to the current illness, a working diagnosis of idiopathic thrombocytopenic purpura was made, for which intravenous immunoglobulin (IVIg) was administered that led to a rapid rise in the platelet count with no adverse events. Subsequently, dengue IgM antibody repeated on day 6 came back positive, confirming dengue. This case report re-emphasises the potential use of IVIg in patients with severe thrombocytopenia in dengue.