Effect of corporate ownership concentration on firm performance has been researched in various fields. We investigate the effect of family and foreign ownership on firm performance – both market and accounting- for companies listed on the Istanbul Stock Exchange-Turkey- from 2005 to 2009. We find a positive relationship between family and foreign ownership and market performance during the period. Our results also show that foreign ownership concentration loses its effect on market performance during 2008-2009 – a period marked by the economic crisis, which might be attributed to the global source of the crisis. Interestingly, effects of family and foreign ownership concentration on firm performance diminish, and even disappear, when performance is measured by using accounting data.