evidence: The committee reviewed nine studies to evaluate the risk of encephalitis or encephalopathy after the administration of vaccines containing diphtheria toxoid, tetanus toxoid, and acellular pertussis antigens alone or in combination. Seven studies (Geier and Geier, 2004; Gold et al., 1999; Isomura, 1991; Kuno-Sakai and Kimura, 2004; Rosenthal et al., 1996; Stetler et al., 1985; Zielinski and Rosinska, 2008) were not considered in the weight of epidemiologic evidence because they provided data from passive surveillance systems and lacked unvaccinated comparison populations. [...] The committee identified five publications reporting encephalitis or encephalopathy after the administration of vaccines containing diphtheria toxoid, tetanus toxoid, and acellular pertussis antigens alone or in combination. Four publications did not provide evidence beyond temporality (Casella et al., 2007; Ehrengut, 1986; Pollock and Morris, 1983; Sivertsen and Christensen, 1996). In addition, two of the publications also reported the administration of additional vaccines making it difficult to determine which, if any, vaccine could have been the precipitating event (Casella et al., 2007; Ehrengut, 1986). Furthermore, Ehrengut (1986) reported that one patient was sick 1 week prior to vaccination. These publications did not contribute to the weight of mechanistic evidence. [...] The committee reviewed three studies to evaluate the risk of arthropathy after the administration of vaccines containing diphtheria toxoid and tetanus toxoid antigens alone or in combination. One study (Stetler et al., 1985) was not considered in the weight of epidemiologic evidence because it provided data from a passive surveillance system and lacked an unvaccinated comparison population.