U.S. millionaires are feeling worse than ever about the economy and the market’s prospects, Spectrem Group announced today.

The firm said its Spectrem Millionaire Index fell five points in October to zero, recording its second-consecutive all-time low. The October drop, the index’s fifth-consecutive decline, kept millionaires on neutral footing for a second month in a row, the first back-to-back neutral readings since the index’s inception in February 2004. Until September, millionaires had been stubbornly optimistic. The millionaire index was mildly bullish from October 2004 to August 2005.

The Spectrem Affluent Investor Index, which measures the investment outlook of households with US$500,000 or more in investable assets, also declined five points in October to a new all-time low of -6, also a neutral reading. The affluent index has been neutral since March 2005.

Millionaires and affluent investors both cited the economy as their greatest concern when asked about the factors most impacting their investment plans.

“The new lows our millionaire and affluent indexes set last month confirm a major shift in the investment outlook of wealthy Americans. Headline after headline of bad news including rocketing energy prices, economic uncertainty, natural disasters and the continuing war in Iraq have significantly eroded the confidence of millionaires and the broader affluent population alike. When asked about their biggest threat to their investment plans, both cited the economy, suggesting they see long-term structural issues at work. This could signal a long winter ahead for the financial markets,” said George Walper Jr., president of Spectrem Group, in a release.

In response to an open-ended question about the factors most impacting their investment plans, affluent investors cited: the economic environment (20%), stock market conditions (16%), household cash flow (8%), retirement (6%), household income (5%), low investment/interest returns (3%), housing and real estate (2%), and jobs/job security (1%). When this same question was last asked in July, the stock market was the top response at 20% followed by economic conditions (9%).

Millionaires expressed similarly high concern about the economy in October with 16% citing it as the No. 1 threat to their investment plans. Next for millionaires were: stock market conditions (15%), household income (8%) and household cash flow (8%).

The Spectrem Affluent Investor Index has a margin of error of plus or minus 6.2 percentage points. Interviews are conducted with the financial decision-makers in households with US$500,000 or more in investable assets. The Spectrem Millionaire Index is based on a subset of the overall survey group.