A growing shellfish industry and a rising concern regarding food safety has increased the importance of understanding the spatial and temporal dynamics of toxic phytoplankton blooms. A global increase of harmful blooms, in terms of frequency, duration, intensity, and distribution has been observed. If these trends are real, regional and local patterns should exhibit similar trends. This study examines whether the frequency, duration, and intensity of saxitoxin-producing bloom events are increasing in Oregon coastal waters. Patterns of shellfish toxicity data were examined using data from samples collected over a fifteen year time period, from 1982-1996, by the Oregon Shellfish Program. The annual frequency of positive saxitoxin samples, the duration of continuous blooms, and the severity of each bloom was determined for each site. It is unclear whether the frequency or duration of outbreaks are increasing at any of the collection sites, however, the post-1990 blooms are more intense than the blooms preceding 1990. There is a strong correspondence between the El Niño Southern Oscillation climatological pattern and the frequency of positive saxitoxin events, particularly for the southern coastal sites. Although the observed trends suggest changes in the patterns of saxitoxin-producing blooms, there are many confounding variables. Factors that may contribute to the observed increase include more extensive monitoring, increased recreational and commercial harvests, unknown nutrient inputs from sources such as deforestation and domestic sewage, and possible warmer ocean temperatures.