Sulfonylurea herbicide-resistant prickly lettuce was discovered in Idaho in 1987. The objectives of these surveys were to determine the change with time in the proportion of sulfonylurea resistant and susceptible prickly lettuce biotypes on the farm where it originally occurred, and to determine the spread of sulfonylurea resistant prickly lettuce beyond its point of origin. On average, the proportion of resistant plants had decreased from 1988 to 1990, a period when sulfonylurea herbicide use was discontinued on the farm. Resistant prickly lettuce plants were found at seven sites away from the original infested farm. Several sites were near the farm along roadsides that had been sprayed with sulfometuron. This study shows that the proportion of resistant prickly lettuce decreased where previously found, but its range increased.