Mature Pinus contorta var. latifolia in the Bitterroot watershed of western Montana bear either predominantly serotinuous cones (cone scales sealed by a resin bond and requiring a heat treatment for opening) or nonserotinous cones. This study investigated the extent to which among-stand variation in serotiny could be explained by environmental variables, estimated fire frequency, and the nature of stand-initiating disturbance. The frequency distribution of serotiny at the stand level was biomodal, with peaks near 25 and 75% serotinous cones. Stand-level serotiny was not related to measured environmental variales and was only weakly related to estimated fire frequency. In contrast, much of the among-stand variation in serotiny could be explained by the nature of the stand-initiating disturbance, with a predominance of serotinuous trees in stands that had the originated from stand-replacing burns and of nonserotinuous trees in those that had originated from disturbances not related to fire. The disturbance regime is highly variable in time and space, and this variability, coupled with gene flow, is an important factor maintaining the polymorphism of cone type in stands.