Infection with Toxocara canis is a common world-wide human helminthiasis, which rarely elicits central nervous system (CNS) impairment. A case-control study to investigate this discrepancy was carried out, in which the cases were 27 adult neurological inpatients for whom a definite aetiological diagnosis was lacking, and for whom positive immunodiagnosis of toxocariasis had been obtained, both in cerebrospinal fluid (CSF) and in serum. Two control groups were used. Controls were adult inpatients with other neurological diseases who had no evidence of T. canis infection of the CNS. Multivariate logistic regression analysis did not reveal any positive relation between case status and clinical signs. A significant association was observed between case status and an elevated CSF cell count. Rural residence, ownership of dogs, and dementia were shown to be risk factors for toxocaral infection of CNS. These results suggest that migration of T. canis larvae in the human brain does not frequently induce a recognizable neurological syndrome but is correlated with the association of several risk factors including exposure to dogs, a status possibly responsible for repeated low-dose infections.