Previous studies suggest cross-reactivity between specific ragweed pollen and melon allergens. This study was designed to clarify the origin of the cross-reactivity between ragweed pollen and the gourd family. One thousand ragweed-allergic subjects were interviewed about the presence of oral allergy syndrome (OAS) induced by melon or watermelon and were divided into reactive to ≤3 seasonal allergen sources or >3 seasonal allergen sources. Patients reporting melon and/or watermelon allergy underwent a skin-prick test (SPT) with fresh melon and, after 2006, also with profilin-enriched date palm pollen extract. Because no IgE reactivity to melon extract was detected in vitro, ELISA was performed using date palm pollen extract, and inhibition experiments were performed using grass pollen, date palm profilin, and bovine serum albumin (BSA) as inhibitors. Six hundred forty-six and 354 subjects reacted to ≤3 seasonal allergens or >3 seasonal allergens, respectively; 4/646 (1%) and 81/354 (23%) reported a history of melon/watermelon-induced OAS (p < 0.0001). Forty-three of 46 (93%) melon reactors scored positive on SPT with the profilin-enriched extract, which was positive in 0/2 (0%) versus 43/44 (98%) reactive to ≤3 or >3 seasonal allergen sources, respectively (p < 0.0001). in vitro, serum from melon-allergic subjects showed a strong IgE reactivity to the profilin-enriched date palm pollen extract, which was abolished by preabsorption with both grass pollen extract and date palm pollen extract, but not by BSA. In ragweed pollen-allergic subjects, melon allergy is most likely associated with cross-sensitization to the plant pan-allergen profilin and not to specific ragweed pollen allergens. This study confirms the association between profilin sensitization and melon allergy.