Measles, mumps, rubella (MMR) vaccination is included in the routine vaccination program in our country. In the past, many children died or were permanently disabled due to measles and its complications. MMR has significantly decreased with routine and widespread use of MMR vaccination. Many adverse effects such as fever, parotitis, vasculitis, pancreatitis, uveitis, subacute sclerosing panencephalitis, 3rd and 6th nerve paralysis and anaphylaxis may develop following MMR vaccination. 'Claw hand defomity' developing after MMR vaccination has not been reported up to date. Claw hand is the motor dysfunction of the ulnar nerve. This paper presents patients who developed pain, fever and local discharge at the injection area and claw hand deformity after receiving MMR vaccination to the distal part of the deltoid muscle. Claw hand deformity did not improve despite medical and surgical treatment. Thus, we suggest that claw hand deformity may be due to an immunologic reaction. There are some misunderstandings about vaccination in our country. Vaccination rates may decrease if they are not clarified.