This Lagos-based study provides an unsupervised grouping of the causes of building collapse in Lagos State Nigeria using purposively obtained data from construction professionals (n=34) in the state. Hierarchical cluster analysis technique and mean scores were used for the analyses. Findings show that the causes of building collapse in Lagos State can be statistically grouped into design and construction-related, policy-related and quality-related causes. The most important causes of building collapse under each of these groups are respectively: poor maintenance culture, change of use of building and use of substandard materials in construction. Government needs to strengthen efforts at monitoring both the design and construction of buildings, starting with fine-tuning building related policies. A holistic approach should be adopted in addressing building material counterfeiting and circulation of substandard construction materials in the study area. Keywords: Building Approval, Building Collapse, Building Failure, Cluster Analysis, Lagos State.