Abstract Objectives. Some parents with a sick infant contact a doctor, while others do not. The reasons underlying such parental decisions have not been thoroughly studied. The purpose of this study was to explore how the actual symptoms in the infant were associated with parent-rated illness, illness severity, and the probability of the parents contacting a doctor. Design. A retrospective questionnaire and a prospective diary study covering 14 months of the participating infants' lives. Setting and subjects. The 194 participating infants were followed for three months prospectively from the age of 11 to 14 months using diary cards, and retrospectively from birth until the age of 11 months by a questionnaire. Results. During the three months of the diary card prospective follow-up, the infants had symptoms on average every second day, and the vast majority (92%) had 10 or more days with at least one symptom; 38% of the infants were reported to have had five or more symptoms for more than five days. Fever, earache, and vomiting were the symptoms most likely to cause parents to rate their infant as ill. Earache was the symptom that triggered doctor contact most immediately. The parent-rated illness severity was strongly related to the tendency to contact a doctor. However, this association was markedly weaker when adjustment was made for the infant not eating normally, having a cough, or running a fever. Conclusion. Specific symptoms such as fever, earache, and vomiting were strongly associated with the probability of parents rating the infant as ill. An earache would cause the parents to contact a doctor. Fever and vomiting were other symptoms triggering doctor contacts. First, these symptoms could cause the parents to want a doctor's expert evaluation of the infant's illness; second, the parents could expect medication to be necessary; or third, it could just be difficult for the parents to handle the ill infant.