The presence of calculus was assessed on the lingual surfaces of the mandibular anterior teeth in a randomly selected group of 63 young adults. The rate of regrowth of calculus after professional prophylaxis was also observed. Twenty-two individuals had supragingival calculus on the mandibular lingual surfaces of their teeth at baseline. Eleven of these individuals demonstrated regrowth of calculus by the end of the study, in spite of repeated professional prophylaxis. Thus, 17.5% of subjects exhibited rapid regrowth of calculus on the mandibular lingual surfaces of their teeth within 2 weeks of professional prophylaxis.