BACKGROUND & OBJECTIVES: The construction industry is a leading contributor to occupational injuries. First Information Reports (FIRs) of Indian Police are a potential data source for construction injuries. The aim of this study was to estimate the completeness of ascertainment of construction site injuries by FIRs. METHODS: This was a two-sample capture-recapture study of construction site injuries sustained in the year 2017 in Delhi, India. The first capture sample was data extracted from FIRs. The second capture sample comprised data extracted from the Employee State Insurance Corporation (ESIC) and the Commissioners of Workmen Compensation. The Chapman estimator was used to estimate, with 95% confidence intervals, the total numbers of fatal and non-fatal injuries. RESULTS: FIRs ascertained 374 injuries (110 fatal and 264 non-fatal) while the combined data of ESIC and workmen compensation claims ascertained 80 injuries (48 fatal and 32 non-fatal). The capture-recapture analysis estimated that 1,011 (95% CI: 873 to 1149) injuries: 258 (95% CI: 221 to 295) fatal injuries and 873 (95% CI: 765 to 1053) non-fatal injuries were sustained in Delhi in 2017. INTERPRETATION & CONCLUSIONS: FIRs ascertain approximately one-third of all construction site injuries. In the absence of any other data source, FIRs may be used as the basis of a construction injury surveillance system, recognizing that any estimates made using these data must be adjusted to allow for the approximately two-thirds of injuries not reported to the police. Further research is needed to identify reasons for some injuries not being reported to the police, in order to help to develop a strategy to improve the completeness of ascertainment of construction site injuries for the future.