The chief executive of children's cancer charity Clic Sargent, Carole Easton, is to leave at the end of April.
Staff were also told last week that the charity's existing reserves of £1.7m would sustain it for only five weeks, and that redundancies would be necessary.
A spokesman for Clic Sargent said Easton had already decided to "pursue other interests" some time ago and hoped to set up a consultancy. She had brought forward her departure date, he said, to help the charity save money in the short term.
The spokesman said the charity's reserves were always at their lowest levels in March, but would pick up later in the year. The charity also had fixed assets of £10m.
"We have the stability to see us through difficult times, but we will have to make cuts in line with our new strategy to eliminate services for which demand is not there," he said. An internal consultation on the redundancies would take about six weeks, the spokesman said. The redundancies would occur at all levels of the organisation, but the numbers involved would not be extensive, he added.