To estimate the concentration in air and the cancer risk of irrigation workers and the public exposed to the total trihalomethanes (TTHMs) in reclaimed water used for landscape irrigation, a probabilistic health risk assessment was conducted through the integrated use of one-dimensional (1-D) and two-dimensional (2-D) Monte Carlo simulations. Before the 2-D simulation, a sensitivity analysis corresponding to the 1-D simulation was carried out to identity the factors most affecting the outputs. The results reveal that the TTHM concentration level and cancer risk for workers' exposure is much higher than that for public exposure in landscape irrigation. Moreover, the most influential factors are quite different for workers' exposure and public exposure. The 2-D Monte Carlo risk analysis result for the workers indicated that the lowest-risk, highest-risk and two critical points for irrigation height are 0.7 m, 1.53 m, 1.4 m and 1.65 m when the mean value of the risk is selected as the reference statistic for risk management. Based on the risk assessment results, different measures can be suggested for the risk control of different populations. Furthermore, the influential variables should be better characterized to improve the accuracy of health risk assessment (C) 2013 Elsevier B.V. All rights reserved.