The Bulgarian social security system underwent significant reforms in the late 1990s, transforming it into a three-pillar structure. The first pillar operates on a pay-as-you-go principle and comprises five distinct funds: the Pension Fund, General Disease and Maternity Fund, the Occupational Accident and Professional Disease Fund, the Unemployment Fund, and the Non-Work-Related Pension Fund. The second pillar is supplementary compulsory pension security, which operates on a fully funded principle. Pension companies manage defined contribution pension plans based on individual accounts. The third pillar is supplementary voluntary pension security, also based on a fully funded principle, allowing individuals to accumulate additional resources to finance supplementary pension benefits. The implemented reforms aimed to address the unfavourable demographic changes expected to unfold in the coming years, which would place significant pressure on the country’s pension system. The establishment of the second and third pillars was expected to enhance the financial stability of the system and increase the adequacy of pension benefits for future generations of retirees. More than two decades later, the demographic structure of the Bulgarian population continues to deteriorate, corresponding to earlier predictions. However, several factors have adversely affected the second and third pillars, preventing them from fully supporting the first pillar as intended. The main aim of this article is to assess the reforms implemented in the Bulgaria’s social security system over the years, the problems encountered, and the solutions required. The focus is on the pension system, as it absorbs the greatest part of the resources and affects the largest portion of the population. The first part of the paper describes the reforms and their expected results, while the second part analyses the current problems of the system and possible future reforms that could improve its long-term sustainability.