The construction industry is assumed to be the most risky and hazardous of all industries due to the frequent high rates of accidents, ill-health and safety risks involving on construction sites. This becomes a perpetual concern to all the stakeholders in the construction industry. Therefore, this study investigates the various causes and effects of accidents on construction sites in Lagos State, Nigeria. Structured questionnaire was used to source the industry stakeholder’s opinions and unstructured interview were used to consolidate their opinions for the data collection. Responses were analyzed and ranked using Likert scaling method. In attempt to reduce the occurrence and severity of construction site accidents to the minimum, findings from the study identify the critical causes of accidents on construction sites and its effects in Lagos State, Nigeria. This paper therefore concludes and recommends amongst others, training and education regarding health and safety, the use of Personal Protective Equipment’s (PPE) by construction workers, ensuring safe working environment and enforcing effective and stricter safety rules against defaulters.