An epidemiologic investigation of a gastroenteritis outbreak in December 1994 indicated that salad consumption during lunch was linked with illness on 2 days (5 December: odds ratio [OR]=3.1, 95% confidence interval [CI]=2.0-5.0; 6 December: OR=3.1, 95% CI=1.9-4.9). Single stool or vomitus specimens from ill students and staff (case-patients) were examined for bacterial and viral pathogens. Small round-structured viruses (SRSVs) were detected by electron microscopy in stool specimens from 9 of 19 case-patients and in vomitus specimens from 3 of 5 case-patients. By reverse transcription-polymerase chain reaction (RT-PCR), the SRSVs were shown to be G-2/P2-B type strain. The nucleotide sequences of RT-PCR products from vomitus and stool specimens of ill students were identical to stool specimens from the ill salad chef. These findings suggest that a single SRSV strain was the etiologic agent in the outbreak that was possibly transmitted to students through consumption of contaminated salad. Epidemiologic investigation in conjunction with molecular diagnostics may enable early identification of sources of infection and improve outbreak control.