Concerning bone and joint diseases therapy of rheumatic synovitis (= radiosynoviorthesis) was introduced in 1952 before clinically relevant diagnostic procedures were developed. Radionuclides of Sr and later on 99mTc phosphonates then started the wide use of bone scintigraphy since > 30 years. The diagnostic methods have an excellent sensitivity for detection of local abnormalities of bone metabolism, the specificity of such studies, however, is low. Modifications of the technique (3-phase-bone-scintigraphy, pinhole collimators, ROI-technique), increasing knowledge of pathological scan patterns and introduction of other radionuclide studies (67Ga, 201Tl, inflammation scans with 99mTc-leukocytes or 99mTc-HIG) as well as 18FDG-PET have increased the specificity significantly in recent years and improvements of imaging systems (SPECT) also increased the accuracy of diagnostic methods in diseases of bone and joints. Therapy of such diseases has made considerable progress: inflamed, swollen joints can effectlively be treated with 90Y-, 186Re, 169Er-colloids or with 165Dy-particles by radiosynoviorthesis. Severe pain due to disseminated bone metastases of cancer or polyarthritis can be controlled by radionuclide therapy with 89Sr, 153Sm-EDTMP, 186Re- or 188Re-HEDP and possibly 117mSn-DTPA with an acceptable risk of myelodepression. Possibilities, technical details and limitations of radionuclide applications for diagnostic and therapeutic purposes must be considered if optimal benefit for individual patients should be achieved. Overall Nuclear Medicine can become an essential element in management of bone and joint diseases. The relationship of Nuclear Medicine to bone and joint pathology is peculiar: In 1952 treatment of rheumatic synovitis by radiosynoviorthesis with 198Au Colloid was started by Fellinger and Schmid (1) before diagnostic approaches to bone pathology existed. Bone scintigraphy was introduced only in 1961 using 85Sr (2) but obviously the unfavourable radiation characteristics of this radionuclide limited it's broad application and 87mSr did not improve this situation (3). Only when 99mTc phosphonates were developed by Subramanian (4) the importance of bone scintigraphy became apparent: The excellent imaging properties of these radiotracers showed, that abnormal bone metabolism could be visualized even before morphological alterations in the skeleton become visible on radiographies or even CT-scans (5). Moreover, proposals made earlier (6, 7) to use 32P or 89Sr for palliation of pain in patients with disseminated skeletal metastases were picked up again and led also to other radiopharmaceuticals (186Re-HEDP, 153Sm-EDTMP, 117mSn-DTPA) which are applied today for the same purpose with very good success (8). Therefore Nuclear Medicine today has a broad program for diagnostic and therapeutic approaches to diseases of bone and joints. In bone scanning the high sensitivity led to inclusion of this method for routine staging and re-staging programs in a variety of cancer forms which have a trend to develop bone metastases (e.g. breast, lung, prostate, melanoma) but the low specificity of abnormal patterns on such scans can impair the diagnostic value of the technique (9). To increase specificity and to define inflammatory lesions, radiotracers used for "inflammation scanning" were introduced such as labeled granulocytes, 99mTc Human Immunoglobuline and others (10-12) but also a simple modification of bone scanning - triple phase bone scintigraphy (13) - was used. Recently the excellent properties of 18F for PET of the skeleton were rediscovered again (14) and emission CT scanning - possibly with overlay with transmission CT or MRT pictures (15) - can enhance the diagnostic impact of radionuclide bone studies.