This follows the announcement of the early retirement, also on health grounds, of Jim O'Neill, the Scottish regional officer of the National Association of Schoolmasters Union of Women Teachers.
Mr Lamont, ironically, was elected to the top SSTA job in 1994 in succession to Alex Stanley, who had himself to bow out early for medical reasons. Mr Lamont is 56 and has been an official in the union since 1981, becoming depute general secretary for nine years in 1985.
The SSTA is now bound by law to invite nominations for Mr Lamont's successor and arrange for ballot papers to be posted to members' homes in the even of a contest. Candidates will be asked to step forward in September with any election likely to take place in November.
Meanwhile Craig Duncan, the SSTA's depute general secretary, becomes acting general secretary; and David Eaglesham, the third union official, temporarily takes over as its number two.