Detection of a target grouping is expedited when the target display is preceded by presentation of an oscillating premask that includes priming elements presented intraphasically and below detection threshold at the display locations subsequently occupied by the target. Five experiments were performed to investigate how priming is affected by both the complexity and the geometry of prime/target forms. Experiment 1 showed that the subjective complexity of different polygons was coded in accord with an objective measure of form complexity. Experiments 2 and 3 revealed oscillatory priming to increase as a function of the subjective complexity of prime/target forms when those forms were regular and predictable. However, Experiments 4 and 5 showed that this relation did not hold when the prime/target forms were irregular and unpredictable. Taken together, it is argued that both subjective complexity and the Pragnanz quality of the prime/target forms come to determine the magnitude of priming. These results are discussed with reference to current physiological hypotheses regarding perceptual organization.