The growth of thin films of chemical vapour deposition (CVD) diamond onto flat samples of pure Zr has been studied using various CVD growth conditions in a hot filament reactor. We find that although growth is straightforward, adhesion of the diamond layer onto the Zr is poor, with the diamond layer often delaminating upon cooling. SIMS depth profiles show this to be due to the presence of a strongly-bonded native oxide on the Zr surface which is not removed in the reducing H2 atmosphere during CVD. This, plus the lack of any substantial carbide interfacial layer to ‘glue’ the diamond onto the surface, together with a poor thermal expansion mismatch between Zr and diamond, and the Zr hcp-to-bcc phase transition at ∼860°C, all lead to poor adhesion. Some of these difficulties can be reduced by depositing at lower temperature (<500°C) at the cost of poorer quality diamond.