A practical method for calculating the pK(a)'s of selenols in aqueous solution has been developed by using density functional theory with the SMD solvation model and up to three explicit water molecules. The pK(a)'s of 30 different organoselenols, 16 with known experimental pK(a)'s, have been calculated by using three different functionals (omega B97XD, B3LYP, and M06-2X) and two basis sets (6-31+G(d,p) and 6-311++G(d,p)). Calculations using omega B97XD and B3LYP with SMD solvation without explicit waters are found to have errors of 3-6 pK(a) units; the errors with M06-2X are somewhat smaller. One explicit water interacting with the selenium reduces the calculated pK(a)'s by 1-2 pK(a) units along with improving the slope and intercept of the fit of the calculated pK(a)'s to experiment. The best results for SMD/M06-2X/6-31+G(d,p) are with one explicit water (MSE = -0.08 +/- 0.37 and MUE = 0.32 +/- 0.37) whereas omega B97XD and B3LYP still have errors larger than 2 pK(a) units. The best results for omega B97XD and B3LYP with 6-31+G(d,p) are obtained by using three explicit waters (MSE = 0.36 +/- 0.24 and 0.34 +/- 0.25, respectively) and a fit to experiment yields a slope of 1.06 with a zero intercept. The errors for M06-2X/6-31+G(d,p) with three explicit waters are significantly larger (-3.59 +/- 0.45) because it overstabilizes the anions. On the basis of the molecules studied here, M06-2X/6-31+G(d,p) with one explicit water and omega B97XD/6-31+G(d,p) and B3LYP/6-31+G(d,p) with three explicit waters and the SMD solvation model can produce reliable pK(a)'s for the substituted selenols.