Limited information exists on the tolerance of processing tomato to postemergence (POST) application of thifensulfuron-methyl. The tolerance of 13 processing tomato varieties, ‘CC337’, ‘H9144’, ‘H9314’, ‘H9478’, ‘H9492’, ‘H9553’, ‘H9909’, ‘N1069’, ‘N1082’, ‘N1480E’, ‘N1480L’, ‘N1522’, and ‘PETO696’, to POST applications of thifensulfuron-methyl at the maximum use rate (6 g ai/ha) and twice the maximum use rate (12 g/ha) for soybean was evaluated at two Ontario locations in 2001 and 2002. At 7 days after treatment (DAT), thifensulfuron applied POST caused 0.2 to 1% visible injury to CC337, H9144, N1082, N1522, and PETO696 at the high rate. H9553, H9909, N1069, and N1480E were the most sensitive to POST thifensulfuron-methyl, with visible injury ranging from 1 to 6% at the high rate. There was no visible injury to H9314, H9478, H9492, or N1480L at either application rate of thifensulfuron-methyl. By 28 DAT, no visible injury was noted to any variety, except for H9909, N1069, and N1480L, which showed minimal (<2%) visible injury. There were no adverse effects on shoot dry weight and marketable yield for any variety at either rate. Although thifensulfuron-methyl applied POST caused minimal and transient injury to the varieties tested, more tolerance trials with other fresh and processing tomato varieties are required to confirm these initial results.