Background Ethyl glucuronide (EtG) in urine is considered a marker of recent ethanol consumption or ethanol exposition. tert-Butanol is primarily used as a solvent and intermediate chemical. Like tert-amyl alcohol, tert-butanol is discussed in Internet forums as ethanol replacement. We discuss false-positive immunological EtG screenings by excretion of different alcohol glucuronides (EtG homologs), mainly tert-butyl glucuronide in urine of a polytoxikomanic in-patient. Methods Three consecutive urine samples from an in-patient with a long history of multiple substance abuse including solvents were analyzed by DRI EtG enzyme immunoassay (ThermoFisher Scientific Microgenics) on a Beckman Coulter AU680 analyzer, an in-house LC–MS/MS for EtG, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl glucuronide, and an in-house headspace GC-FID of free congener substances methanol, 1-propanol, 2-butanone, 2-butanol, isobutanol, 1-butanol, 3-methyl-1-butanol, 2-methyl-1-butanol, and additionally for ethanol, acetone, 2-propanol, tert-butanol and 2-methyl-2-butanol. Results EtG immunoassay yielded two positive urine samples (0.2 and 0.6 mg/L or 0.1 and 0.2 mg/g creatinine; cut-off 0.1 mg/L) which were tested EtG negative by LC–MS/MS (cut-off 0.1 mg/L) but positive for tert-butyl glucuronide (3.7 and 27.1 mg/L), 2-butyl glucuronide (1.1 and 3.5 mg/L), and 2-propyl glucuronide (0.1 and 0.4 mg/L). Headspace GC-FID detected tert-butanol (0.97 and 4.01 mg/L), methanol (0.96 and 0.62 mg/L), 2-butanone (0.84 and 1.65 mg/L), and 2-butanol (0.04 and 0.09 mg/L), but no ethanol and no 2-methyl-2-butanol. Conclusion Cross-reaction of EtG homologs, mainly tert-butyl glucuronide after suspected tert-butanol or isobutane abuse, explains the false-positive EtG immunoassay findings. Future investigations could address the usefulness of alcohol glucuronides (EtG homologs) in urine as (a) biomarkers of an exposition to alkans or their corresponding alcohol metabolites and (b) as markers for using “old”-well known alcohols like tert-butanol or tert-amyl alcohol as easy to obtain, cheap, potent and “undetectable” ethanol replacements or “New” Psychoactive Alcohols.