The Lagos megacity is a unique conurbation where a significant proportion of the population and economic activities  is  concentrated in the greater Lagos metropolitan area with critical human-environmental conditions. In this study we present the pattern of social vulnerability to flooding across the Lagos metropolis and argued that the pattern substantially reflects the pattern and severity of flooding impact on people across the metropolis. Twenty nine social indicators and experiences including poverty profile, housing conditions, education, population and demography, social network, and communication, among others, were considered. The data were collated through field survey and subjected to principal component analysis. The results were processed into raster surfaces using GIS for social vulnerability characterization at local government areas (LGAs) and neighborhood levels. The results suggest the social status indicators, neighborhood standing and social networks indictors, the indicators of emergency responses and security, and the neighborhood conditions, in that order, are the most important determinants of social vulnerability.  Six of the 16 LGAs in metropolitan Lagos have high social vulnerability. Neighborhoods that combine poor social status indicators and poor neighborhood standing and social networks are found to have high social vulnerability whereas other poor neighborhoods with strong social networks performed better.