Background Toxoplasma gondii and Toxocara are common parasites that infect humans globally. Our aim was to examine the relationship between T. gondii and Toxocara infection and cognition.

Methods Multivariate logistic regression was used to test the association of T. gondii and Toxocara seropositivity on indices of cognitive function (a word list learning trial with delayed recall from the Consortium to Establish a Registry for Alzheimer’s Disease, an animal fluency test (AFT) and a digit symbol substitution test (DSST)) among 2643 adults aged 60 years and older in the 2011–2014 National Health and Nutrition Examination Survey.

Results Seropositivity to T. gondii or Toxocara were both associated with lower scores in all three cognitive function measures examined in univariate analyses. Except for the DSST, these associations were not significant after adjustment for age, gender, race and Hispanic origin, poverty level, education, US birth status, depression and hypertension. On stratification to account for significant interactions, Toxocara seropositivity was associated with worse scores on the AFT among those born outside the USA, worse scores on the DSST among those aged 60–69 years, female, Hispanic and with a high school diploma or less. Lower DSST scores with Toxocara infection was greater for adults living below compared with at or above the poverty level.

Conclusions Seropositivity to these parasites, particularly to Toxocara, may be associated with diminished cognitive performance in certain subgroups of older adults.