This pilot study enrolled 20 children between the ages of 11 and 17 months in Imperial County, California to assess children's pesticide exposure and residential proximity to agricultural fields. We compared parental self-report of residential proximity to agricultural fields to measurements using global positioning system/geographical information system (GPS/GIS) technology, and we assessed the relationship between residential proximity to agricultural fields and a biomarker of organophosphate (OP) pesticide exposure. Questionnaires were administered twice, 4 weeks apart, to determine self-reported residential proximity to agricultural fields. Urine samples were collected at each contact to measure OP metabolites. Actual residential proximity to the closest agricultural field and number of fields was within 1 mile to the west were measured using GPS/GIS. Self-report of living proximity to agricultural fields agreed with GPS/GIS measurement 75% of the time during the initial interview, compared to 66% agreement during the second interview. Presence of urinary metabolites suggests that OP exposure was ubiquitous: creatinine-adjusted total urinary dimethyl values ranged from 1.60 to 516.00 microg/g creatinine, and total diethyl ranged from 2.70 to 134.84 microg/g creatinine. No association was found between urinary OP metabolites and residential to field proximity. These results suggest that initial self-report of living proximity to agricultural fields may be more accurate than follow-up self-report. Limitations in this pilot study prevent determination of whether self-report is an accurate measure of proximity.