As we enter the third millennium, we are witnessing an unprecedented rapid expansion of the population of older persons in both the developed and developing world. The total worldwide aged population (aged 60 and older) is projected to rise from 605 million in 2000 to 1.2 billion in 2025 and to nearly 2 billion in 2050. To study the process of population ageing in Bulgaria and Balkan countries and to reveal its main characteristics, similarities and differences as compared to other European countries. Primary information was obtained from the European Database "Health for all", the European Public Health Information Network for Eastern Europe and the US Census Bureau International Database. Total, male and female old and youth dependency ratios and ratio of people over 65 to 0-14 years were calculated and trends were followed for 30 years. Countries were ranked and compared with Europe and East European countries. From 1970 to 1999 the old dependency ratio increased dramatically in Bulgaria (14.2-23.6%), Greece (17.2-24.7%), Romania and Slovenia. The ratio of old to young people surpassed 100% in Greece (107.3%, for female 122.6%) and in Bulgaria (99.7% and 116.8%, respectively). Albanian and Turkish populations differ substantially from the other Balkan countries. Population ageing creates great socio-economic and health problems--slower economic growth, lack of young labour force, higher tax charges on working-age population, etc. The process in Balkan countries is aggravated by the rise of inflation, unemployment and other socio-economic factors. All Balkan countries face multiple challenges posed by population ageing. Most of them experience the same demographic tendencies as for market economy countries even though their economic development is far worse. This is especially true for Bulgaria.