It is shown here that carbamazepine (CBZ) would undergo direct photolysis and reaction with *OH as the main phototransformation pathways in surface waters. Environmental lifetimes are expected to vary from a few weeks to several months, and predictions are in good agreement with available field data. Acridine (I) and 10,11- dihydro-10,11-trans-dihydroxy-CBZ (V) are the main quantified phototransformation intermediates upon direct photolysis and *OH reaction, respectively. The photochemical yield of mutagenic I from CBZ is in the 3−3.5% range, and it is similar for both direct photolysis and *OH reaction: it would undergo limited variation with environmental conditions. In contrast, the yield of V would vary in the 4−8.5% range depending on the conditions, because V is formed from CBZ by *OH (9.0% yield) more effectively than upon direct photolysis (1.4% yield). Other important photointermediates, mostly formed from CBZ upon *OH reaction, are an aromatic-ringdihydroxylated CBZ (VI) and N,N-bis(2-carboxyphenyl)urea (VII). Compounds VI and VII are formed by photochemistry and are not reported as human metabolites; thus, they could be used as tracers of CBZ phototransformation in surface waters. Interestingly, VI has recently been detected in river water.