in The X-Men (Marvel, 1963 series) #88 (June 1974)
in The Official Marvel Index to the X-Men (Marvel, 1987 series) #2 (July 1987)
in Marvel Masterworks: The X-Men (Marvel, 2003 series) #4 ([October] 2004)
in X-Men: First Class Giant-Size Special (Marvel, 2008 series) #1 (December 2008)
in The X-Men Omnibus (Marvel, 2009 series) #2 ([April] 2011)Sources for letters credit are The Marvel Comics Index (Olshevsky 1981), The Official Marvel Index to the X-Men (Olshevsky 1987), The Official Marvel Index to the X-Men (Ward 1994), and Official Index to the Marvel Universe (Vandal et al. 2009).
in The X-Men (Marvel, 1963 series) #88 (June 1974)
in The Titans Annual (World Distributors, 1976 series) #1977 (1976)
in Marvel Special (Marvel Italia, 1994 series) #14 (Luglio 1998) [page count uncertain]
in Marvel Masterworks: The X-Men (Marvel, 2003 series) #4 ([October] 2004)
in X-Men: First Class Giant-Size Special (Marvel, 2008 series) #1 (December 2008)
in The X-Men Omnibus (Marvel, 2009 series) #2 ([April] 2011)Professor X secretly replaced by Changeling through issue #43.
in Amazing Adventures (Marvel, 1979 series) #3 (February 1980)
in The Marvel Saga (Marvel, 1985 series) #4 (March 1986)
in Marvel Special (Marvel Italia, 1994 series) #4 (Luglio 1995)
in Marvel Masterworks: The X-Men (Marvel, 2003 series) #4 ([October] 2004)
in The X-Men Omnibus (Marvel, 2009 series) #2 ([April] 2011)
in The X-Men Omnibus (Marvel, 2009 series) #2 ([April] 2011)