We present an intuitive, fast and accurate interactive segmentation method for extracting and visualizing a large range of objects from 3D medical images. Our method combines a general deformable subdivision-surface model with a novel sketch-line user initialization process. The model is simply and precisely initialized with a few quick sketch lines drawn across the width of the target object on several key slices of the volume image. The smooth surface constructed using these lines is extremely close to the shape of the object boundary, making the model’s task of snapping to this boundary much simpler and hence more likely to succeed in noisy images with minimal user editing. Our subdivision surface model provides a foundation for precise user steering/editing capabilities and simple, intuitive user interactions are seamlessly integrated with advanced visualization capabilities. We use our model to segment objects from several 3D medical images to demonstrate its effectiveness.