Non-permissible concentration of fluoride salts in ground water induces various anomalies in human beings. Bhagalpur city’s ground water contains 1–2 ppm of fluoride. Its genotoxic effects were assessed in Swiss albino mice Mus Musculus. 25% (50 mg/l) and 50% (100 mg/l) concentrations were found to increase the frequency of abnormal cells by 10.33 and 19.33% and chromosome abnormalities by 10.33 and 20.00% in bone marrow cells. The increase in frequency of chromosome anomaly was mainly due to significant increase in individual type, viz. chromatid breaks, gaps and acentric fragments. The effect is dose dependent. Fluoride salts present in the ground water might have interfered the phagocytosis and produce oxygen free reactive radicals that attack the nucleophilic sites of the DNA leading to the loss of important gene segments responsible for cell growth and the ageing.