Donald Nicolaisen, the chief accountant of the Securities and Exchange Commission, has announced that he will leave the SEC next month to return to the private sector.

Nicolaisen was appointed to the post in September 2003 by former chairman William Donaldson; his departure creates another important slot for chairman Christopher Cox to fill. Cox is already looking for directors to head the divisions of market regulation and investment management.

Since he joined the commission, Nicolaisen has had his hands full. He has been heavily involved in the SEC’s decision to postpone the implementation of Sarbanes-Oxley Section 404 several times, and he has even supported efforts by small companies to scale back certain provisions. Nicolaisen also played a key role in efforts to expense the value of stock options.

In a press release, the SEC credited Nicolaisen with forging a close working relationship with the Public Company Accounting Oversight Board and working closely with the Financial Accounting Standards Board and international agencies toward convergence of accounting standards. “Don Nicolaisen has served with distinction during challenging times, and has met every challenge — most notably by establishing landmark new protections for investors during the implementation of the Sarbanes-Oxley Act,” said Cox, in a statement.

Prior to joining the commission, Nicolaisen was a senior partner at PricewaterhouseCoopers LLP. He joined the firm’s predecessor Price Waterhouse in 1967; between 1988 and 1994, he led the firm’s national office for accounting and SEC services and was a member of FASB’s Emerging Issues Task Force. He later chaired the firm’s financial services practice for broker-dealers, investment banking, mutual funds, banking, insurance, and real estate. Nicolaisen was elected to the firm’s board of partners in 1994.