The authors present analyses of data from three independent clinical series and controls indicating an association between working in occupations with probable medium to high exposure to extremely low frequency (<300 Hz) electromagnetic fields and sporadic Alzheimer's disease. Case-control analyses were carried out using data from patients examined at the following locations: the Department of Neurology, University of Helsinki, Helsinki, Finland, 1982–1985; the Koskela Hospital in Helsinki, 1977–1978; and the University of Southern California site of the Alzheimer's Disease Research Center of Los Angeles and Orange Counties, 1984–1993. The predominant occupations among medium (2–10 mG or >10 mG intermittently) to high (>10 mG or >100 mG intermittently) exposed cases were seamstress, dressmaker, and tailor. The results appear to be independent of education, and the sex-combined odds ratios for the three series are quite homogeneous 2 9, 3.1, and 3.0. The odds ratio for the three series analyzed together is 3.0 (p < 0.001), with a 95% confidence interval of 1.6–5.4. The odds ratio for women is 3.8 (p < 0.001), with a 95% confidence interval of 1 7–8.6. The most obvious, possibly etiologically relevant exposure is that of electromagnetic fields, which may have biologic plausibility because they may adversely influence calcium homeostasis and/or inappropriately activate immune system cells such as microglial cells, initiating events that result in neuronal degeneration.