Purpose: The aim of this work is to compare the ability of whole body MRI including diffusion study with that of 99m Tc-Methylene Diphosphonate Scintigraphy to detected skeletal metastases in patients with breast and lung cancer. Patients and methods: 60 patients comprising 38 females and 22 males ranging in age from 30 to 60 years with a mean age of 48.1 years (mean age 47.3 years for females and 49 years for males) were enrolled in the study. 29 females are histopathologically proven cases of breast malignancy, 9 females and the 22 males are histopathologically proven cases of lung cancer. The patients were referred from Oncological departments to perform the whole body MR study and bone scan at Ain Shams University hospitals MRI units and a private center during the time interval from December 2008 till December 2012. All patients were subjected to both whole body MRI and bone scintigraphy. The whole body MRI was mainly obtained using 4 contiguous coronal stations for body coverage using the body coil and 2 contiguous sagittal stations for the spine using T1W FSE and STIR sequences. 48 out of 60 patients toke IV contrast and post contrast T1W imagaes with fat suppression were taken. The MRI examinations were performed using a superconducting 1.5 Tesla magnet (Achieva: Philips Medical Systems).   Standard skeletal Scintigraphy was performed using a planar one phase technique (delayed phase). The examination was done 2-3 hours after IV injection of  technicium 99m labeled Methylene Diphosphonate with a maximum dose of 20 mCi.   Results: 42 patients out of 60 were positive for metastases based on histopathological verification or follow up. On MRI, 39 patients had metastases, 3 were false negative, 12 were true negative and 6 were false positive. On bone scan, 35 were true positive, 7 were false negative, 4 were false positive and 14 were true negative. Based on lesion detection, on comparing bone scan to WB-MRI with and without diffusion, bone scan  had an overall sensitivity of 85.6%, specificity 67.5 %, PPV 61.7% and NPV 66.3%, while WB-MRI had statistical values of 73.4%, 68.8%, 78.1% and 62.6% respectively. On adding DWI, values raised to 88.9%, 82.9%, 93% and  69% respectively. Quantitative analysis of DWI was also included in this study revealing an overlap between the Low ADC values of red marrow and metastasis at the range of 0.61 to 0.69 x10^-3 mm²/sec and then between metastasis and other benign pathological marrow entities at the range of 0.9 to 1.03 x 10^-3 mm²/sec. WB-MRI also detected 64 soft tissue metastatic lesions which became 71 lesions on adding DWI with a distribution of hepatic, pulmonary, brain, adrenal, lymph nodes, pleural, leptomeningeal and renal lesions.   Conclusion: we don't think that WB-MRI should replace bone scan in the quest for skeletal metastases. However, we believe that WB-MRI should be the modality of choice when both skeletal and soft tissue metastases are suspected and in the follow up of a known metastatic patients for adequate coverage of both skeletal and soft tissue structures combined with qualitative and quantitative features of DWI helping assess tumors at cellular levels even prior to gross morphological changes verifying response to therapy as early as possible sparing patients precious time  from drifting with delayed decision making.