This paper seeks to explain the century-long trend of falling proportion of females in the Indian population. In the first part, some clues to the puzzle are unearthed by identifying the age groups, regions and social groups of the estimated 21 million females gone 'missing' between 1901 and 1991. In particular, it is shown that overtime there has been a convergence of the sex ratios of adults and children, and female-male ratios declined in regions and social groups where the adult sex ratios were substantially higher than the child sex ratios. In the first half of the last century, the overall sex ratio declined because of the decline at adult ages, especially at age 40 and over. After independence, the decline has been more concentrated at ages under 15. However, census data should be interpreted with caution because improving quality of age data on children can produce a spurious trend of falling sex ratios at certain childhood ages. In the light of these disclosures, the second part of the paper reviews the plausible explanations for the long-term trend of falling female-male ratio in India.
