Assuming a somatic mosaicism detection rate of 5% (Kozlowski et al., 2007) and given that no mutation was identified in TSC1 or TSC2 by the sequence analyses in 13.21% of individuals with TSC, we conclude that fewer than 1% of persons with TSC have somatic mosaicism for a TSC1 or TSC2 mutation. This evidence concerns the gene TSC1 and tuberous sclerosis.