This pilot study aimed to elucidate whether or not mothers who receive neonatal home visits tend to suffer from depressive disorders during the first postpartum year and to examine what kinds of factors were related to the postnatal depression observed in these mothers. The subjects consisted of 70 Japanese mothers who received neonatal home visits and completed the 1-year study. At their first visit, the health visitors asked about their personal backgrounds and early postpartum mood, and depression was assessed by a Japanese translation of the Edinburgh Postnatal Depression Scale (EPDS). At 12 months postpartum, a diagnostic interview using the Structured Clinical Interview for DSM-IV (SCID) was performed to confirm the maternal diagnosis by a psychiatrist. An assessment of infant development using the Denver Developmental Screening Test (DDST) was administered to each infant by a psychologist. Nineteen mothers (27%) were categorized as having had a new onset of depression (12 major depressive disorders and seven depressive disorders not otherwise specified). In comparison to the non-depressed mothers, infant-related health problems that required either outpatient treatment or hospitalization were significantly related to postnatal depression. Pediatric diseases in infants did not always precede their mother's depression. The extra burden of caring for a sick infant tends to increase the risk of developing postpartum depression. As a result, neonatal home visits by health visitors may therefore be a potentially crucial opportunity to provide emotional support, particularly for mothers with the extra burden of having to care for sick infants.