The scalability of an information system describes the relationship between system ca-pacity and system size. This report studies the scalability of Microsoft Lync Server 2010 in order to provide guidelines for provisioning hardware resources. Optimal pro-visioning is required to reduce both deployment and operational costs, while keeping an acceptable service quality.All Lync servers in the test setup are virtualizedusingVMware ESXi 5.0 and the system runs on a Cisco Unified Computing System (UCS) platform. The scenario is a typical hosted Lync deployment with external users only and telephone integration. While several companies offer hosted virtual Lync deployments and the Cisco UCS platform has a rich market share, Microsoft’s capacity planning guides don’t provide help for such a deployment scenario or hardware platform. This report consequently fill an information gap.The scalability is determined by using empirical measurements with different work-loads and system sizes. The workload is determined by the number of Lync end-users and the system size varies from 1/4 to 4/4 Cisco UCS blade server. The results show a linear scaling in the range of 1/4 to 4/4 blade servers. The processor is found to be the main bottleneck resource in this deployment. Themean opinion score (MOS) aswell as the front end server utilization are the best metrics formonitoring service quality.