Recent globalization and integration of capital markets made international diversification more difficult for many investors and caused correlations between the securities to increase, especially during the times of adverse economic conditions. This paper argues that markets, which have cointegrating relationship and follow common trend in a long time horizon, cannot contribute much to portfolio diversification. Therefore, investors, who are willing to invest for long-term, should rather choose cointegration analysis instead of usual correlation approach for portfolio diversification purposes because the former is more appropriate for long-term. Thus, this paper took a perspective of Lithuanian investor and conducted cointegration analysis with 8 other country equity indices over a period 2000-2011 in order to find out which markets Vilnius OMX is cointegrated with. This paper should be useful to investors who seek to diversify internationally and look for a long-term perspective, and who are willing to go beyond the conventional portfolio diversification methods.