An inefficient market refers to the fact that a stock price deviate from the true value. Such an market inefficiency is the “January effect”. The “January effect” is the phenomenon were the stock market performs better in January than in any other month. This is a seasonal anomaly which should not exist according to the market efficient hypothesis. The “January effect” is a phenomenon that today cannot be fully understood. Thus, many studies have been made on the “January effect”. The effect have been studied across the world since the 1970s, and Rozeff & Kinney (1976) where the first to conclude a seasonal anomaly where January was the responsible month for abnormal returns. Further studies, such as the study by Keim (1983), concludes that the “January effect” is largely a small firm phenomenon. There are several indicators that are said to be the reason for the “January effect”, such as the tax-loss selling hypothesis tested by Reinganum (1983), none of the findings have however been fully supported. Claesson (1987) conducted a study of the “January effect” on the Swedish Stock market in 1987. Her findings was in accordance with other findings across the world, thus the “January effect” did exist in Sweden during 1980s. My study focus on the “January effect” in Sweden and whether or not it is a present phenomenon, thus increasing the contemporaneity of the “January effect”. I base my study on Claesson’s, but I also use  various studies that have been made across the world about this seasonal anomaly. The purpose of the study is to increase the Swedish contemporaneity of the “January effect”. I want to increase the knowledge and understanding of this seasonal anomaly in today’s stock market in Sweden. The study will be of use for both professional and unprofessional investors and can be of use in portfolio strategy decision making.´ In order to make conclusions and to make the research profound I have used theories such as “The-small-firm in January effect” and the “Tax-loss selling hypothesis”. Earlier studies by researchers have been used in order to give an understanding and in order to make a reliable study. I have  used a sample between the years 2003-2011 from the NASDAQ OMX Nordic Stock Exchange. The Sample focus on the Stockholm Stock Exchange in order to determine the existence of the effect in Sweden. The sample is raw data from three different indices which then have been analyzed through Excel. The finding from this study is that there is a “January effect” present on the Stockholm Stock Exchange today. This seasonal anomaly can be seen for small firms listed on the Small Cap at the Stockholm Stock Exchange. Small firms present abnormal returns during January that is consistent over the sample period. Small firms consistently outperforms large firms during the month of January, an outperformance that cannot be seen in any other month during a given year. The study also concludes that December is a strong month, especially for large firms. This creates a discussion on the exploration of the market inefficiency and calls for further studies on the matter. Further evidence of such an exploration can be seen on the last five days of trading in December for small firms. Small firms consistently present high returns during the last trading days of December, thus strengthen the theory that there is an exploration of the market inefficiency.