Background: Due to its use of ionising radiation, the field of nuclear medicine is a unique and significant part of medical diagnostics and patient treatment. The aim of this study was to assess the internal exposure of nuclear medicine employees to radioiodine 131I and technetium 99mTc as well as to assess the external exposure doses. Material and Methods: The radioiodine 131I and technetium 99mTc contents in the thyroid of staff members (about 100 persons) dealing with these radionuclides have been measured in four departments of nuclear medicine. The measurements were conducted with a portable detection unit for in situ measurements of radioiodine and technetium. High sensitivity environmental thermoluminescent dosimeters (TLD) were used to measure the external exposure dose. Results: The average values and ranges of radioiodine 131I activity measured in the thyroids of all of the medical units' employees were: 83 Bq (range: 70-250 Bq), 280 Bq (range: 70-4000 Bq), 275 Bq (range: 70-1000 Bq) for technical staff, nuclear medicine staff and hospital services staff, respectively. The mean value of technetium 99mTc content in the thyroids of nuclear medicine staff was approximately 1500 Bq (range: 50- -1800 Bq). External exposure dose rates were in the range of 0.5-10 μGy/h. Conclusions: The calculated average effective dose for particular person caused by the inhalation of radioiodine 131I is below 5% of 20 mSv/year (occupational exposure limit). Med Pr 2013;64(5):625–630