The company's adjusted earnings missed analysts' estimates, but its revenue topped Wall Street's expectations. Shares fell more than 4 percent in afternoon trading.
FXCM earned $3 million, or 11 cents per share, for the three months ended Dec. 31. In the same period a year ago, it made $3.2 million, or 21 cents per share.
FXCM said that there were 12 cents per share in deferred tax benefits recognized by its Japanese subsidiary in the year-ago period.
Excluding special items, adjusted earnings were 13 cents per share.
Revenue dipped 1 percent to $108.1 million, partly because revenue from referring broker fees fell.
Analysts polled by FactSet expected earnings of 15 cents per share and $104.4 million in revenue.
Active accounts climbed 5 percent to 170,930.
For all of 2012, FXCM Inc. earned $9 million, or 37 cents per share. That's down from $12.7 million, or 77 cents per share, a year earlier. Revenue rose slightly to $417.3 million from $415.6 million.
Shares of FXCM lost 57 cents, or 4.2 percent, to $13.05. The stock has traded between $8.50 and $13.99 over the last 52 weeks.