Measurements of heterogeneous crystallization (scaling) have been performed using an intrinsic exposed-core optical fiber sensor (IECOFS). The IECOFS showed several advantages over the conventional techniques of scale detection: turbidity and electrical conductivity, including insensitivity to the presence of suspended crystals caused by homogeneous crystallization and the ability to monitor scale deposition under continuous supply conditions. Calibration of the IECOFS, to quantify scale deposited on a given surface, and the limitations of the technique are also presented.