Abstract We evaluate the efficacy of the stable isotope composition of precipitation and plant waxes as proxies for paleoaltimetry and paleohydrology in the northern tropical Andes. We report monthly hydrogen (δ 2 H p ) and oxygen (δ 18 O p ) isotope values of precipitation for an annual cycle, and hydrogen isotope values of plant waxes (δ 2 H wax ) obtained from modern soils along the eastern and western flanks of the Eastern Cordillera of Colombia. δ 2 H p , δ 18 O p , as well as the unweighted mean δ 2 H wax values of n ‐C 29 , n ‐C 31 , and n ‐C 33 n ‐alkanes in the eastern flank show a dependence on elevation ( R 2 = 0.90, 0.82, and 0.65, respectively). In stark contrast, the stable isotope compositions of neither precipitation nor plant waxes from the western flank correlate with elevation ( R 2 < 0.23), on top of a negligible ( p ‐value >0.05) correlation between δ 2 H wax and δ 2 H p . In general, δ 2 H wax values along the eastern flank of the Eastern Cordillera seem to follow the trend of a simple Rayleigh distillation process that is consistent with studies elsewhere on the eastern side of the Andes in South America. Neither δ 2 H p nor δ 18 O p , and therefore δ 2 H wax , offer reliable estimates of past elevations in the western flank, due perhaps to water vapor source mixing, evaporation overprint, contrasting plant communities, and/or differences in evapotranspiration. Thus, δ 2 H wax is only reliable for paleohydrology and paleoaltimetry reconstructions on the eastern flank of the Andes, whereas interpretations based on δ 2 H p and/or δ 18 O p west of the highest point of the Eastern Cordillera need to consider mixing of moisture sources in addition to precipitation amount.