This paper uses a new calendar design implemented in the Guatemalan Survey of Family Health to analyze diarrheal and respiratory illness among children. The calendar provides a much richer description of child illness and treatment behavior than do conventional data typically collected in health interview surveys. The resulting estimates reveal that Guatemalan children experience high rates of diarrheal and respiratory illness and that these illnesses often involve multiple symptoms that only partially overlap one another. In addition, estimates from the calendar demonstrate that the measurement of illness frequency is fairly complex and that classification of illness into distinct categories may not always be feasible or meaningful. Results regarding treatment behavior indicate that the vast majority of illnesses are treated and that mothers almost always receive advice regarding their children’s illnesses from relatives. On the other hand, health providers are sought for advice and treatment in only about one-third of illnesses. When families do seek providers, they are more likely to rely on biomedical ones — especially pharmacists, doctors and personnel at health posts and centers — than traditional practitioners. By far, the most common form of treatment — recommended by both relatives and providers — consists of readily available Western medicines. In contrast, the use of traditional remedies appears to be relatively low.