OBJECTIVES: To study how concentrated the Finnish pharmaceutical market is in certain medicine groups. During the last decade the Finnish authorities have implemented different acts to increase the competition in the pharmaceutical market. METHODS: We examined the concentration of the pharmaceutical market by using the Herfindahl-Hirschmann Index. We calculated the index for 12 different medicine groups in 2002-2008. Ten of these groups were prescription medicines and two were self-care medicines. The index is calculated by summing up the squares of the market shares for all the firms operating in the medicine group. It is important that all medicines in each group can be substituted to each other. The index value varies between 1/n - 1, n=firms. Greater value of the HHI indicates greater concentration. If HHI is below 0.18 there is no concentration at all. RESULTS: In 2002 the total HHI average for the 12 groups was 0.30 as in 2008 it was 0.22. In anti-dementia drugs the index dropped from 0.48 to 0.23. In triptans the index dropped from 0.40 to 0.17. The smallest index was seen in antiallergics. In 2002 the index in this group was 0.14 and in 2008 it was 0.12. In 2008 the most concentrated group according to the index was the protone pump inhibitors. The index in this group was 0.38. CONCLUSIONS: From 2002 to 2008 the concentration in medicine groups has clearly diminished. The difference between these groups is partly due to patents. The two self-care medicine groups used in the study are clearly less concentrated than the prescription medicine groups. However, the average for all 12 groups is 0.22 and exceeds the index point of 0.18. This indicates that among the medicine groups used in calculations the market is still concentrated.