A needle guide system for use with an ultrasound probe, the system comprising: (i) a surface marking guide; and (ii) a needle guide; (i) the surface marking guide including: (a) an attachment portion for attaching the marking guide to an ultrasound probe, and (b) either means for marking the surface when the ultrasound probe is held against the surface; or means for identifying to a user where to mark a surface when the ultrasound probe is held against the surface; and (ii) the needle guide including: (a) a base to support the needle guide on the surface; (b) one or more features on the base for alignment with marks made on the surface; and (c) a needle support mounted on the base and having a needle channel through which a needle can extend, the needle channel having a known position and orientation relative to the base and characterized in that the needle guide system further comprises sensors for measuring the orientation of the guides in space, wherein (i)(c) the surface marking guide includes a sensor for measuring the orientation of the guide in space and (ii)(d) the needle guide comprises a corresponding sensor for measuring the orientation of the needle guide, wherein the orientation of the surface marking guide can be noted and the needle guide can subsequently be positioned to have the same orientation as the surface marking guide; (i) a surface marking guide; and (ii) a needle guide; (i) the surface marking guide including: (a) an attachment portion for attaching the marking guide to an ultrasound probe, and (b) either means for marking the surface when the ultrasound probe is held against the surface; or means for identifying to a user where to mark a surface when the ultrasound probe is held against the surface; and (a) an attachment portion for attaching the marking guide to an ultrasound probe, and (b) either means for marking the surface when the ultrasound probe is held against the surface; or means for identifying to a user where to mark a surface when the ultrasound probe is held against the surface; and means for marking the surface when the ultrasound probe is held against the surface; or means for identifying to a user where to mark a surface when the ultrasound probe is held against the surface; and (ii) the needle guide including: (a) a base to support the needle guide on the surface; (b) one or more features on the base for alignment with marks made on the surface; and (c) a needle support mounted on the base and having a needle channel through which a needle can extend, the needle channel having a known position and orientation relative to the base and characterized in that the needle guide system further comprises sensors for measuring the orientation of the guides in space, wherein (i)(c) the surface marking guide includes a sensor for measuring the orientation of the guide in space and (ii)(d) the needle guide comprises a corresponding sensor for measuring the orientation of the needle guide, wherein the orientation of the surface marking guide can be noted and the needle guide can subsequently be positioned to have the same orientation as the surface marking guide; (a) a base to support the needle guide on the surface; (b) one or more features on the base for alignment with marks made on the surface; and (c) a needle support mounted on the base and having a needle channel through which a needle can extend, the needle channel having a known position and orientation relative to the base and characterized in that the needle guide system further comprises sensors for measuring the orientation of the guides in space, wherein (i)(c) the surface marking guide includes a sensor for measuring the orientation of the guide in space and (ii)(d) the needle guide comprises a corresponding sensor for measuring the orientation of the needle guide, wherein the orientation of the surface marking guide can be noted and the needle guide can subsequently be positioned to have the same orientation as the surface marking guide; and characterized in that the needle guide system further comprises sensors for measuring the orientation of the guides in space, wherein (i)(c) the surface marking guide includes a sensor for measuring the orientation of the guide in space and (ii)(d) the needle guide comprises a corresponding sensor for measuring the orientation of the needle guide, wherein the orientation of the surface marking guide can be noted and the needle guide can subsequently be positioned to have the same orientation as the surface marking guide;