We present a new approach to anomaly detection based on unsupervised niche clustering (UNC). The UNC is a genetic niching technique for clustering that can handle noise, and is able to determine the number of clusters automatically. The UNC uses the normal samples for generating a profile of the normal space (clusters). Each cluster can later be characterized by a fuzzy membership function that follows a Gaussian shape defined by the evolved cluster centers and radii. The set of memberships are aggregated using a max-or fuzzy operator in order to determine the normalcy level of a data sample. Experiments on synthetic and real data sets, including a network intrusion detection data set, are performed and some results are analyzed and reported.