Di(2-ethylhexyl) adipate (DEHA) is a plasticizer and phthalate substitute used in various consumer products. Relevant population exposures have to be assumed. In this study we describe the determination of three specific side chain-oxidized monoester metabolites of DEHA, mono-2-ethyl-5-hydroxyhexyl adipate (5OH-MEHA), mono-2-ethyl-5-oxohexyl adipate (5oxo-MEHA), and mono-5-carboxy-2-ethylpentyl adipate (5cx-MEPA) in human urine as potential biomarkers of DEHA exposure. After enzymatic hydrolysis, urine samples were analyzed by online turbulent flow chromatography for matrix depletion and analyte enrichment coupled to liquid chromatography-electrospray ionization-triple quadrupole-tandem mass spectrometry (online-SPE-LC-MS/MS). For quantification stable isotope dilution was applied with limits of quantification of 0.05 μg/L for 5cx-MEPA and 5OH-MEHA, and 0.1 μg/L for 5oxo-MEHA. Method accuracies (relative recoveries) were between 92 and 109%, and relative standard deviations <5%. We investigated the applicability of the method for internal DEHA exposure assessment in six volunteers who had consumed food wrapped in commercial PVC-cling film containing DEHA and in two small pilot populations without known DEHA exposure (44 pregnant Brazilian women and 32 German adults). In the cling film experiment, we could quantify all three metabolites in all post exposure urine samples, with 5cx-MEPA being most prominent (0.30-10.2 μg/L), followed by 5OH-MEHA (0.12-4.31 μg/L) and 5oxo-MEHA (0.12-2.84 μg/L). In the Brazilian and German samples we could detect DEHA exposures in 43 and 9% of all samples, again with 5cx-MEPA as the most prominent metabolite. Based on validation and pilot biomonitoring results, the method has proven appropriate for DEHA biomonitoring and will be applied in future metabolism and population studies.