A number of previous studies suggested the presence of deleterious amino acid altering nonsynonymous single-nucleotide polymorphisms (nSNPs) in human populations. However, the proportions of deleterious nSNPs among rare and common variants are not known. To estimate these, >77,000 SNPs from human protein-coding genes were analyzed. Based on two independent methods, this study reveals that up to 53% of rare nSNPs (minor allele frequency (MAF)<0.002) could be deleterious in nature. The fraction of deleterious nSNPs declines with the increase in their allele frequencies and only 12% of the common nSNPs (MAF>0.4) were found to be harmful. This shows that even at high frequencies significant fractions of deleterious polymorphisms are present in human populations. These results could be useful for genome-wide association studies in understanding the relative contributions of rare and common variants in causing human genetic diseases.