In the Tropics, papular urticaria (PU) is a common skin hypersensitivity disease caused by insect bites. At the sea level, mosquito is identified as the main cause of this condition. Risk factors for developing PU are not yet clear, neither several aspects of its pathogenesis. We sought to determine the relationship among dwelling exposure to potential causal insects, mosquito sensitization and PU presentation. As part of an epidemiological survey to estimate the prevalence of PU in Cartagena, a tropical city of Colombia, a nested case-control study was designed. Mosquito collection at home was done during 2 consecutive days in 120 children with papular urticaria and 112 without disease. Traps for fleas and bedbugs were also installed. Specific IgE to Aedes aegypti extract was determined by ELISA in a sub-sample of 59 cases and 72 controls. The cut-off point to define sensitization (0.12 OD) was calculated as the mean+2SD of the optical density (OD) values obtained from non-sensitized subjects' sera. Mean age in cases and controls was 3.9 ± SD 1.3 vs. 4.1 ± SD 1.2, respectively. Mosquito collection at home was frequent and there was not association between its presence at home and disease presentation (82% in cases vs 84% in controls, p=0.65). The two identified mosquito species were A. aegypti (68%) and Culex quienquefasciatus (45%), and the distribution of them were also similar between patient and controls. Flea species (Ctenocephalides canis and Pulex irritans) were found in only seven dwellings (3%). The frequency of sensitization to mosquito extract was 36% in patients and 33% in controls (p=0.79), respectively. There was no difference in mean mosquito specific-IgE values between groups (p=0.69). The level of exposure to mosquitoes is not associated with the presentation of PU. Sensitization to A. aegypti is common in this environment, but not related to this disease. Since a delayed cellular response is a hallmark of PU, this aspect must also be investigated.