Launched in 1996, the iShares MSCI Mexico Investable Market Index Fund ( EWW) is currently the only pure play ETF available for investors looking for access to the U.S.' southern neighbor. Sector exposure is in line with the economy. Telecommunications account for 35% of assests, followed by 23% in consumer staples, 14% in materials, 13% in consumer discretionary and 8% in industrials. Although the fund is designed to track the broad Mexican market through an index consisting of 45 holdings, its performance is largely dependent on the success of a small number of these constituents. Carlos Slim's telecommunications firm, America Movil ( AMX), accounts for nearly a quarter of the fund's total portfolio. Other top holdings include Wal-Mart de Mexico ( WMMVY) and cement giant Cemex ( CX). Together, these top holdings make up 40% of the fund's index. EWW's Performance has remained negative through the first part of 2010, but its growth in the most recent one-year period ending Feb. 23 has been impressive. In that time, the fund has managed to gain more than 100%. Given the top-heavy nature of EWW, I would advise investors looking to hold this fund to keep exposure small. Also, it is essential that investors continually monitor the performance of the instrument and the holdings dominating its index. If any of these top weighted companies see a volatile move, its effect on EWW's performance will be significant. Stay tuned for a look at Chile later today. -- Written by Don Dion in Williamstown, Mass.