OBJECTIVE To describe a modification of the index of clinical consequences of untreated dental caries [pulpal involvement, ulceration, fistula and abscess (PUFA/pufa) index] to pulpal involvement-roots-sepsis (PRS/prs) and to compare the two indices using the example of caries in primary molar teeth in children aged 6-8 years. METHODS The study sample included 542 children aged 6-8 years, from five randomly selected schools in the Bialystok District, Poland. The occurrence of clinical consequences of untreated caries in deciduous molars using the pufa and prs indices was evaluated. Data were analysed to express the prevalence, the experience and the distribution of particular pufa and prs codes in the sample population. The differences in layout of the pufa and prs components were expressed. RESULTS The response rate was 77.6%. The prevalence of the clinical consequences of untreated caries was 40.77%, mean pufa and prs were the same (0.85 ± 1.33). According to the pufa index, the following mean values were obtained: p = 0.79, u = 0.01, f = 0.04 and a = 0.01. For the prs index, the mean values were as follows: p = 0.45, r = 0.35 and s = 0.05. CONCLUSIONS The proposed prs index was a useful epidemiological instrument for the evaluation of the clinical consequences of untreated caries in the surveyed population. The PRS instrument could be a good alternative to the PUFA index.