Feline infectious peritonitis (FIP) frequently results in death in cats. It is caused by a mutated, highly contagious coronavirus, and it is more common in indoor cats in multicat households. A complex interaction between the coronavirus and the feline immune system causes disseminated vasculitis, which is the hallmark of FIP. New tests are being developed, but the antemortem diagnosis of FIP continues to be difficult and frustrating. Current treatments are crude and involve supportive care and immunosuppression. Minimizing exposure is the best method of preventing infection.