An episode of group C streptococcal colonization occurred in a newborn nursery. Because these organisms were sensitive to bacitracin in the concentration used in the disk method, they were presumptively identified as group A streptococci. This was interpreted as the onset of a nursery outbreak of group A streptococcal infection. The presence of bacitracin-sensitive group C streptococci in a potentially significant clinical situation emphasizes the importance of performing Lancefield classification before positively identifying organisms as group A streptococci.