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<i>Listeria monocytogenes</i> may persist in food production environments and cause listeriosis. In Norway, a product of concern is the traditional and popular fermented fish product &#8220;<i>rakfisk</i>&#8221;, which is made from freshwater salmonid fish by mild-salting and brine maturation at low temperatures for several months. It is eaten without any heat treatment, and <i>L. monocytogenes</i>, therefore, poses a potential hazard. We investigated the effect of salt and temperature on the growth of <i>L. monocytogenes</i> in <i>rakfisk</i> during the 91 days of maturation. The amounts of organic acids produced during fermentation were too low to inhibit growth of <i>L. monocytogenes</i>. Temperature was clearly the most important parameter for controlling <i>L. monocytogenes</i>. At 7 &#176;C, approximately 2 log growth was observed during the first 14 days of fermentation, and the level of <i>L. monocytogenes</i> thereafter remained constant. At 4 &#176;C, only a little growth potential of the pathogen was recorded. We also investigated the effect of the anti-<i>Listeria</i> bacteriophage P100 on <i>rakfisk</i> with added <i>L. monocytogenes</i>. The phage was introduced to the <i>L. monocytogenes</i>-inoculated fish before fermentation, and an average of 0.9 log reduction was observed throughout the fermentation period. This is the first study of <i>L. monocytogenes</i> behavior in <i>rakfisk</i> and points to possible measures for increasing the product safety.