Clearwire ended fourth quarter 2012 with approximately 9.6 million total subscribers, down 8% from 10.4 million subscribers at the end of fourth quarter 2011. The subscriber base consists of approximately 1.4 million retail subscribers and 8.2 million wholesale subscribers, reflecting 9,000 retail net subscriber additions and 915,000 wholesale net subscriber losses during fourth quarter 2012. The decline in wholesale subscribers, which consist primarily of Sprint 3G/4G smartphone customers, is primarily due to the discontinuation of postpaid WiMAX offerings by Sprint.
Retail cost per gross addition (CPGA) was $155 in fourth quarter 2012 compared to $259 in fourth quarter 2011. The year over year improvement is primarily due to lower retail selling expenses associated with our no-contract offering and higher gross adds, partially offset by increased equipment subsidies. Retail churn was 5.0% in fourth quarter 2012, up from 3.9% in fourth quarter 2011. The increase in churn is primarily due to an increase in subscribers on no-contract plans, which were fully launched in first quarter 2012.
Full year 2012 Adjusted EBITDA improved by $157.0 million year over year to a loss of $(156.9) million. Adjusted EBITDA in fourth quarter 2012 was a loss of $(46.0) million, representing a $68.5 million decline compared to fourth quarter 2011 Adjusted EBITDA of $22.5 million. The decrease is primarily due to lower revenue in fourth quarter 2012 compared to the prior year period.
Cash, cash equivalents and investments (invested primarily in U.S. Treasury securities) as of December 31, 2012 was approximately $868.6 million, a sequential decrease of $315.1 million from September 30, 2012. The sequential decrease primarily reflects the fourth quarter payment of our semi-annual interest payment and cash payments for capital expenditures and operating expenses, which exceeded the cash inflows during the period (primarily from Sprint and our retail business). As compared to December 31, 2011, cash, cash equivalents and investments decreased by $239.0 million.