This paper evaluates use of the Threshold of Toxicological Concern (TTC) approach to assess safety of botanical preparations that may contain potentially genotoxic constituents, based on estimation of the fraction that may be genotoxic. A database of 107 chemical constituents of botanicals was compiled and their potential for genotoxicity evaluated from published data. Forty-three constituents met the criteria for potential genotoxicity. Concentration data on their occurrence in plants provided 2878 data points; the majority were in the low ppm level (range 0.00001–139,965 ppm, by dry weight). Weibull models of the quantitative distribution data were used to calculate 95th percentile values for chemical concentrations, analysing the dataset according to their presence in botanicals (i) as a single chemical, (ii) as two or more chemicals from the same chemical group, or (iii) as two or more chemicals from different chemical groups. The highest 95th percentile concentration value from these analyses was 1.8%. Using the TTC value of 0.15 μg/person per day for potentially genotoxic substances proposed in 2004, this value of 1.8% was used to derive an adjusted TTC value of 10 μg of plant material on a dry weight basis/person per day for assessment of potentially genotoxic substances in botanicals.