This 18-month-old male received his forth DTaP vaccine and his first hepatitis A vaccine on 9/26. Within hours, he developed erythema, swelling, and heat at the injection site. The swelling increased over the next few days and he developed a low grade fever. On 9/30, he developed a rash on his torso that his mother described as small pimple-like lesions. On 10/1, the rash became more severe and urticarial and covered his entire body. His fever increased to 39.4. He was started hydroxyzine and a 5-day course of prednisone 1 mg/kg/day. His rash and fever improved, but returned to the previous level as soon as the prednisone was stopped. After that, he had symptoms on and off where every few days he had high fevers up to 40, an urticarial rash, and joint swelling that included both wrists and ankles, the dorsum of both feet, and index and thumb of one hand. The symptoms lasted for about 3 days and then he would have 1 or 2 days where he felt a little better, but not back to baseline. The high fevers were treated with ibuprofen and acetaminophen. At a Rheumatology Clinic visit on 10/17, it was determined that the patient's symptoms were not secondary to a rheumatologic disease, given no history of arthralgia and normal laboratory tests, including a CBC, ESR, as well as normal compliment levels, but probably secondary to a serum sickness reaction from his DTaP  vaccine. He was admitted to the hospital 10/22-10/23 for worsening of his previously mentioned symptoms as well as worsening facial swelling. At an Allergy Clinic appointment on 10/27, his rash and pruritus had temporarily resolved. At another Allergy Clinic appointment on 11/7 he was still afebrile and was symptom free except for some minor scattered hives. The Allergist concurred that the patient's clinical course was consistent also with a serum sickness reaction as it seemed to be lessening over a long period of time. The Allergist recommend that the patient receive no more DTaP or Hepatitis A vaccines and discussed the need for a future Td booster with consideration for patch testing to TD vaccine. The patient had received all previous vaccines with no problem. Of note, he received his first 3 DTaP vaccines in New Jersey and the forth dose was the first one that he received in California. Per the mother, the vaccines used in New Jersey were from a different manufacturer than those used in California. Summary. Serum sickness reaction secondary to DTaP  vaccine.  12/5/08 Reviewed PCP medical records 10/2-10/24/2008 and also included hospital medical records & consultant redcords. FINAL DX: Hives, allergy to DTaP. Records reveal patient experienced swelling of ankles & wrists & welts all over on 10/2.  Dx w/hives & allergic reaction.  Tx w/antihistamine.  Improved.  RTC 10/9 w/fever, rash & dx w/recurrent hives & fever.  RTC 10/13 w/swelling of joints & fever.  Tx w/antihistamines & referred to Rheumatology.  RTC 10/21 w/red throat, serous OM & few hives.  RTC 10/22 w/fever, hives, serous OM.  12/5/08 Reviewed Hospital medical records of 10/22-10/23/2008. FINAL DX: fever of unknown source; urticaria. Serum sickness reaction from DTaP. Records reveal patient expereinced intermittent fevers, joint swelling & urticaria.  Tx w/steroids, antihistamines.  Rheumatology, ID consults done.  Improved w/treatment & d/c to home.  Referred to Allergy consult as outpatient.    12/12/2008 Reviewed Rheumatology medical records of 10/17/08 FINAL DX: allergic mediated rash secondary to DTaP. Records reveal patient experienced recurrent urticaria & swelling of hands/feet. Did not feel symptoms were a result of a rheum process.