In February 1983 De Boer was nominated as Mayor of Haarlemmermeer, he resigned as a Member of the House of Representatives the same day he was installed as mayor, taking office on 13 March 1983. In September 1985 De Boer was appointed as Secretary-General of the Ministry of Welfare, Health and Culture, he resigned as mayor on 1 October 1985 and was installed as secretary-general, serving from 1 January 1986 until 16 October 1995. In October 1995 De Boer was nominated as chairman of the executive board of the Hospitals association (NVZ), he resigned as secretary-general the same day he was installed as chairman on 16 October 1995.
