OBJECTIVE: To analyze whether a positive family history of dementia (PFHD) is more common in sporadic CJD (sCJD) than in healthy/population controls and to study associated risk factors. PATIENTS/METHODS: Six hundred and eighty-five sCJD patients and 659 sex-/age-matched controls were included. A PFHD in parents/grandparents/siblings was evaluated. The PRNP M129V polymorphism and ApoE genotype in sCJD with/without PFHD were determined by PCR. RESULTS: PFHD was found in 12.1% of sCJD patients and 5.6% of controls (p<0.001). No significant difference in M129V polymorphism was found between sCJD with and without PFHD. Thirty-six percent of sCJD patients with PFHD, 26% without PFHD and 19% of healthy controls had at least one ApoE4 allele. Compared to controls, ApoE4 allele frequency (p=0.005) and proportion of ApoE4 allele carriers (p=0.019) were significantly higher in sCJD with PFHD. INTERPRETATION: A higher frequency of the ApoE4 allele in sCJD with a PFHD could be indicative of an additional risk factor in CJD.