Fog deposition, precipitation, throughfall, and stemflow were measured in a windward tropical montane cloud forest near Monteverde, Costa Rica, for a 65-day period during the dry season of 2003. Net fog deposition was measured directly with the eddy covariance method and amounted to 1.2 ± 0.1 mm day−1 (mean ± standard error). Fog water deposition was 4–7% of incident rainfall for the entire period. Stable isotope concentrations (δ18O and δ 2H) were determined in a large number of samples of each water component. Comparisons between direct fog deposition measurements and the results of a mass-balance model using the stable isotopes as tracers indicated that the latter might be a good tool to estimate fog deposition in the absence of direct measurement under many (but not all) conditions. At 506 mm, measured water inputs over the 65 days (fog plus rain) fell short by 46 mm compared to the canopy output of 552 mm (throughfall, stemflow, and evaporation). The discrepancy is attributed to underestimation of rainfall during conditions of high wind.