Despite a number of serious case reports of mango dermatitis, no attempts at the identification and quantification of allergenic 5-alk(en)ylresorcinols in mango fruits have so far been made. Therefore, total alk(en)ylresorcinol content and relative homologue composition in 13 mango peel samples and 7 samples of mango pulp were determined by HPLC and LC-MS/MS analyses. Furthermore, mango puree and nectar prepared on pilot plant scale were also analyzed and compared with commercially available thermally preserved products. Depending on cultivar, alk(en)ylresorcinol contents ranged from 79.3 to 1850.5 mg/kg of dry matter (DM) in mango peels and from 4.9 to 187.3 mg/kg of DM in samples of mango pulp. The profile of alk(en)ylresorcinols was found to be highly characteristic, with an average homologue composition of C15:0 (6.1%), C15:1 (1.7%), C17:0 (1.1%), C17:1 (52.5%), C17:2 (33.4%), C17:3 (2.4%), C19:1 (2.1%), and C19:2 (0.8%). Mango puree samples prepared from peeled and unpeeled fruits revealed contents of 3.8 and 12.3 mg/kg of fresh weight, respectively. Content and homologue composition were not significantly affected during puree processing and thermal preservation. In nectar samples prepared from peeled and unpeeled fruits, contents of 1.4 and 4.6 mg/L, respectively, were found.