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It depends on a lot of factors. If you are in a challenging and demanding fortune 500 environment, it should not hurt you. If you are promoted fairly frequently, it's also a justification for a long term tenure. If you have been subject to frequent change, like increasing levels of responsibilities, assignments to different business units and divisions, that's also a plus. The concern that most employers have regarding long term employment with one company, is a resistance to change and new challenges. However, if your circumstances mirror what was previously discussed, then those concerns are alleviated.