Background: Zoledronic acid (ZOL) is an important component of therapy for patients with metastatic bone disease (MBD) to reduce the risk of skeletal-related events (SREs). We evaluated overall survival (OS) in patients with MBD secondary to solid tumours included in placebocontrolled ZOL trials. Patients and methods: Exploratory analyses were performed using databases from three randomised trials of ZOL versus placebo. 1126 patients (ZOL, n=731; placebo, n=395) with complete baseline data for 18 predefined parameters were evaluated for OS. Relative risks (RRs) with 95% confidence intervals were assessed using stratified and adjusted Cox regression models. Baseline covariates defining patient populations with significantly different effects of ZOL treatment on OS (identified by stepwise backward elimination) were included in multivariate models. Results: Although OS was similar between the overall treatment groups, ZOL significantly improved OS in the subset of patients (n=423; 38%) with elevated baseline NTX (Z100 nmol/mmol creatinine; RR, 0.692; P=.0028). Notably, this effect was independent of SRE prevention. Additional covariates associated with OS benefits with ZOL (e.g., low albumin, SRE history, elevated lactate dehydrogenase, shorter cancer duration) were characteristic of advanced disease. Conclusion: These exploratory analyses suggest a beneficial effect of ZOL on OS in patients with highly aggressive or advanced MBD.