Rod-shaped gold nanoparticles ('nanorods') have recently attracted widespread attention due to their unique optical properties and facile synthesis. In particular, they can support a longitudinal surface plasmon, which results in suspensions of them having a strong extinction peak in the upper visible or near-infrared parts of the spectrum. The position of this peak can be readily tuned by controlling the shape of the rods. In addition, the surface of the nanorods can be functionalized by a very wide variety of molecules. This has led to interest in their use as selective biomarkers in biodiagnostics or for selective targeting in photothermal thearapeutics. Here, we review the recent advances in the use of gold nanorods in these applications. Additionally, the information available regarding their biocompatibility is discussed.