An introducer assembly (60) is provided with a dilator tip (40) which has at least one portion (46) which is asymmetric in transverse cross-section, preferably being flattened or oval. A dilator tip (40) which is asymmetric over at least a part of its length gives the tip different flexure characteristics in different radial directions (54, 56). This provides advantages in trackability of the dilator tip (40) and thus of the introducer assembly (60) as well as providing for self-orientation of the dilator tip (40), useful in orienting medical devices or treatment tools.
