European and US stocks have suffered one of the worst quarterly falls for the markets in the past decade.
Stocks dropped broadly on Friday in fresh signs that Europe's debt problems and the US economy continue to languish.
The Dow Jones, Standard & Poors (S&P) 500 and Nasdaq each lost more than 12 per cent this quarter, the first time that has happened since the financial crisis crested at the end of 2008.
Wall Street's main Dow Jones index dropped 240.60 points, or 2.2 per cent, to 10,913.38.
The broader S&P 500 index shed 28.98, or 2.5 per cent, to 1,131.42.
The Nasdaq composite index fell 65.36, or 2.6 per cent, to 2,415.40.
Markets have been wracked this summer by growing fears about a possible default by Greece and the increasing likelihood of a global recession.
The S&P 500, the benchmark for most US stock mutual funds, has lost 14.3 per cent since July 1, the start of the third quarter.
"The market has really seen some damage this quarter," said Mike Hurley, portfolio manager of Highland Trend Following Fund.
The weakness appears to be the start of a longer decline, Hurley said, because bonds are increasing in value and interest rates are low.
Traders also are selling commodities such as oil, which would lose value in an economic downturn.
"Lower interest rates and commodity prices are definitely an indication that the market thinks economic activity is going to be weak," Hurley said.
Stocks in France, England and Germany fell on the latest signs of discord among European leaders.
Germany's DAX lost more than 25 per cent during this period, one of the hardest hit over the past three months.
Germany and France proposed managing the region's shared currency through meetings of national leaders, rather than by centralised institutions.
The head of the European Commission balked at the proposal.
Persistent squabbling over financial policy has been a major obstacle to achieving a lasting solution to Europe's debt crisis.
Many European leaders and traders believe Greece will default in the coming weeks or months.
Traders have reacted strongly to news and rumours out of Europe about how the crisis is being addressed.
"Greece is being hit by a cascade of bad economic news from around the world," Jacob Kirkegard from the Peterson Institute for International Economics told Al Jazeera.