Reinforced concrete frame structures constitute a major portion of the building stock of Pakistan. In 2005, Kashmir earthquake exposed the current deficient local design and construction practices in Pakistan. It is hypothesized that inhomogeneity of concrete in general and faulty construction practices in Pakistan cause huge uncertainties in parameters affecting strength, serviceability and seismic assessment results for structures in this country. The aim of this study is to assess the vulnerability of existing reinforced concrete (RC) building stock of Pakistan with respect to a stochastic analysis of the parameters affecting the built infrastructure. For this purpose, typical building characteristics with uncertainties are identified. The probability density functions of material and geometric parameters are defined for these building characteristics. These functions are then used to account for the uncertainty in modelling of structural configurations. Structural response is evaluated through static pushover analysis and vulnerability curves for different structural configurations are derived using the framework developed for deficient RC buildings. The performance of buildings is evaluated in different seismic zones as classified in the new Building Code of Pakistan (BCP-SP 2007). Selected buildings performed satisfactorily in Zones 1, 2A and 2B. Buildings in Zones 3 and 4 are found to be more vulnerable.