A severe avian reovirus (ARV) outbreak occurred in a young broiler flock with 25,000 birds at 2-weeks old in north China in May 2023. Lameness was initially observed in approximately 10% chickens of the flock at that time, and rapid onset lameness and splay legs were subsequently seen in the entire flock; over 70% of the flock was affected at 19 days of age. We conducted a field investigation on this poultry farm 2 days later, when the young broiler flock was 21 days of age. The affected birds were severely lame and suffered swollen joints and watery droppings, and many were unable to walk. During the field visit, we collected various samples including dust from various locations inside the flock house, environmental swabs, watery droppings, and bird cloacal swabs for diagnostic investigation of suspected ARV pathogen. In addition, more than a dozen sick birds from the flock were randomly selected and necropsied on site for examination of gross lesions and tissue collection. On testing these flock swab samples and bird tissue specimens by real-time reverse transcription polymerase chain reaction (rRT-PCR) and virus isolation (VI), 23 out of the 27 flock swab samples and all 12 sick birds were confirmed positive for ARV.