The aim of this study was to describe the medication calculation skills of nurses in Finland. We tried to ascertain how nurses evaluate their own medication calculation skills and how these self-evaluations are associated with various background factors and the actual level they score in a calculation test. In the spring of 2000, nurses (n = 546) in one Finnish university hospital completed a questionnaire specially developed for this study. The instrument included structured questions, statements and a medication calculation test. The response rate was 56%. Data analysis was based on descriptive statistics. The nurses found the mathematics and dosage calculation easy and interesting but the pharmacology difficult. They evaluated their own mathematical and dosage calculation skills as sufficient, although it had certain shortcomings. The youngest nurses (20-29 years) evaluated their mathematical and dosage calculation skills as sufficient and they also succeeded in the calculation test. Basic (High School) education was associated with better calculation skills. The findings of this study support the need and importance of checking and maintaining one's medication calculation skills.