Background: Cesium-137 is one of those man-made radioactive nuclides that results from human activities including open air nuclear weapons testing, nuclear accidents, operation of nuclear reactors and has a relative long half-life, higher water solubility, high fission yield, relatively high volatility and a close physic-chemical similarity to potassium that makes it a dangerous radioactive element in the human environment and is a hazardous byproduct of nuclear fission. Cesium-137 being a γ-emitter is also a potential carcinogen. Materials and Methods: A total of 100 soil samples were collected from various sites in Islamabad and its suburbs for the assessment of the presence of Cesium-137 in the environment. Spectroscopy of the collected samples for determination of aforementioned radionuclide was performed using a computer based High Purity Germanium (HPGe) detector. Results: The highest value of Cesium-137 was found to be 57.0±4.2 Bq/kg in samples collected from Nilore, a suburb of Islamabad. Conclusion: The presence of Cesium-137 in all samples is clear evidence that the studied area is contaminated either due to past fallout or ongoing nuclear activities in this area. Cesium-137 was found in higher concentration for this area than the reported values in literature for the rest of country, but not to an alarming level. However, local concerned authorities must pay attention to avoid the development of possible future health hazards to the residents of this area.