Abstract This paper presents a study of the relationship between levels of community-reportedinfectious diseases (measles, rubella, influenza, mumps, scarlet fever, hepatitis A, and salmonella) and rates of neural tube defects (anencephalus and spina bifida) in Los Angeles County during 1968–77. Cases of anencephalus and spina bifida were ascertained from vital records, and rates of the infectious diseases under study were obtained from county Communicable Disease reports. No statistically significant correlation was observed between the quarterly trends of infectious diseases and neural tube defects over the study period. No relationships were observed between the seasonal patterns of neural tube defects and the diseases. Using periods of elevated disease activity to determine hypothetical high- and low-risk periods for conceiving infants with these defects, none of the rate ratios was significantly elevated above unity for any of the infectious diseases under study. Because of limitations in study design, accuracy of case identification, and accuracy of disease reporting, our results cannot be interpreted as disproving a role for these infectious diseases in the etiology of neural tube defects. Nevertheless, our results do indicate that such associations as may exist are not strong enough to be reflected in community health data.