Campylobacter spp. is the most common gastrointestinal pathogen worldwide with a very low reported incidence in Italy. In November of 2013, local and national public health authorities investigated an outbreak caused by Campylobacter jejuni among children in a kindergarten in Northern Italy. A case was defined as a child who had diarrhea with a laboratory-confirmed diagnosis of C. jejuni between 11 and 30 November. Stool samples from the kindergarten kitchen staff and environmental samples from the kitchen were examined for enteric pathogens. As food leftovers were not available, the menu logbook of the refectory was reviewed to identify a possible source of the outbreak. C. jejuni strains were tested for antimicrobial susceptibility and subtyped by pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). We identified 20 cases among 247 schoolchildren (attack rate = 8%), all who reported having lunch in the kindergarten. The stools from the kitchen staff as well as the environmental samples were negative for enteric pathogens. The identified outbreak strains (n = 5) were sensitive to all of the antimicrobials tested; the first four strains showed an identical PFGE profile, whereas the fifth strain showed a PFGE pattern similarity of 89%. Using MLST, all five strains were assigned to a single sequence type (ST), ST451 (clonal complex, CC21); this was the first identification of ST and the third reported outbreak of C. jejuni in Italy. Molecular typing confirmed that most of the cases belonged to a clonal cluster supporting the hypothesis of a common source; however, the source was not identified. Due to a delayed start of the investigation, it was not possible to perform any microbiological evaluation of the food consumed.