A large proportion of international real estate investment is concentrated in the office markets of the world s largest cities. However, many of these global cities are also key financial services centres, highlighting the possibility of reduced economic diversification from an investor s perspective. This paper assesses the degree of synchronization in cycles across twenty of the world s largest office markets, finding evidence of significant concordance across a large number of markets. The results highlight the problems associated with commonalities in the underlying economic bases of the markets. The concentration of investment also raises the possibility of common flow of funds effects that may further reduce diversification opportunities.