From the Microsoft Q&A Section of their site.
Q. How long will my Microsoft certification be valid?
A. Today, most of our Microsoft Certified Technology Specialist (MCTS), Microsoft Certified IT Professional (MCITP), and Microsoft Certified Professional Developer (MCPD) exams retire when Microsoft discontinues mainstream support for the related technology. The certification will still appear on your transcript but will be listed in an inactive section with an expiration date. In most cases, an upgrade path, which allows candidates to earn the certification with fewer exams (usually one), will be available for individuals who hold the certification on the previous version of the technology.
The legacy Microsoft certifications, such as Microsoft Certified Systems Engineer (MCSE) and Microsoft Certified Systems Administrator (MCSA), currently do not expire, but some may no longer be awarded because all exams are retired or because Microsoft has ended extended support for the technology. In most cases, individuals who hold the certification on the previous version of the technology can earn the certification on the next version of the technology with one upgrade exam.
To maintain the relevance and value of our certifications and ensure that candidates possess up-to-date skills on technologies that are constantly changing, recertification may be necessary for some certifications. In these cases, the certification will remain valid as long as the candidate continues to recertify at appropriate intervals.
Note that Microsoft reserves the right to retire exams and certifications as well as change our recertification policy at any time.
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