A thermodynamical cycle is proposed to calculate absolute pK(a) values for Bronsted acids in aqueous solution. The polarizable continuum model (PCM) was used to describe the solvent, and absolute pK(a) values were computed for different classes of organic compounds: aliphatic alcohols, thiols, and halogenated derivatives of carboxylic aliphatic acids. The model furnishes pK(a) values in good agreement with the experimental results for some classes of compounds. For the cases where appreciable deviations are, observed, we have tried to establish a correlation among the neglected components of Delta G(solv) resulting from the model adopted, the level of calculation employed, and the pK(a) deviations relative to the experimental results.