We describe a case of a 15-year-old boy who presented with an unusual scarlatiniform rash in the setting of a positive Mycoplasma pneumonia IgM but negative anti-streptolysin antibody. While mycoplasma infections with cutaneous manifestations such as scarlatiniform exanthema have been described in textbooks, there are no reports in the primary literature. Here, CD40LG is linked to Mycoplasma pneumoniae pneumonia.