Since the emergence of mRNA COVID-19 vaccines, various secondary cutaneous reactions have been reported. 1,2 Commonly observed cutaneous reactions include local injection-site erythema or discomfort, as well as urticarial and morbilliform eruptions. [1][2][3] Less frequent sequalae include perniosis, herpes simplex virus reactivation, flares of psoriasis, and pityriasis rosea-like reactions. 1,4 We report a 66-year-old female with hypertension, hypothyroidism, and hypercholesterolemia, who developed firm, tender, 4-5 cm deep-seated nodules on the right superior medial popliteal fossa and bilateral anterior tibia, 10 days after receiving the first dose of the COVID-19 Moderna mRNA-1273 vaccine (Figure 1). The patient provided informed consent to publish this case. By the time of medical evaluation, some nodules had begun to fade, and the patient was otherwise well, without symptoms of COVID-19 infection. The clinical impression was erythema nodosum (EN), and incisional biopsy of the nodule at the right superior medial popliteal fossa was performed 3 days later. One day prior to biopsy, COVID-19 PCR nasopharyngeal testing was negative. Histologic sections demonstrated widened subcutaneous septae containing an inflammatory infiltrate of lymphocytes, neutrophils, eosinophils, and histiocytes, compatible with EN. Routine hematologic and chemistry studies were unremarkable.Erythrocyte sedimentation rate, C-reactive protein, and circulating rheumatoid factor were normal. Anti-nuclear antibodies, anti-doublestranded DNA antibodies, anti-streptolysin antibodies, and hepatitis B