Illnesses caused by an usual strain of Salmonella Newport, were linked to eating almonds purchased at Costco warehouses in the northwestern United States, in early 2004. Ultimately illnesses would be found throughout the USA and Canada. The almonds were processed by Paramount Farms, a California grower and processor. Paramount Farms almonds were sold in bulk, and under a variety of labels. An investigation at the Paramount Farms processing plant failed to reveal a source for this unusual outbreak strain of Salmonella. The almond consumption history of a case in Tennessee was of particular interest, in that there was no obvious link to Paramount Farms almonds. During 2003-2004, five percent of the almonds processed at Paramount Farms were purchased from outside sources. Traceback of these almonds revealed one common handler and three common huller shellers. Environmental sampling conducted as part of this traceback effort did not reveal the outbreak strain of Salmonella, but did reveal several other Salmonella serotypes. Raw almonds were confirmed as a potential source of Salmonella. Current harvesting and processing practices limit the possibility of reduction or elimination of Salmonella in almonds without the addition of further treatment, such as heat. Paramount Farms voluntarily recalled 13 million pounds of raw almonds. This outbreak had persisted for many months before the source was determined. Illnesses related to the outbreak first occurred in January, 2002. The last noted illnesses occurred in April, 2004.