The latest Wellcome Witnesses to Contemporary Medicine series has been published (link is external), focussing on Seasonal Affective Disorder. The variation of mood with the seasons has been acknowledged for a long time. It was in 1984 that the term Seasonal Affective Disorder (SAD) was first used in a paper by Norman Rosenthal and colleagues at the National Institute of Mental Health in Bethesda, MD. This Witness Seminar looked at the research leading up to that paper and the thirty years of subsequent investigations into the disorder which affects a significant proportion of the population.