The firm said underlying profits jumped by a better-than-expected 23% to £72.2m in the year to 25 Dec as UK deaths rose by 7% last year - the largest annual increase since 1952.
The number of deaths in the UK last year jumped to 588,000 compared to 550,000 in 2014, according to the Office for National Statistics.
The UK's only listed undertakers, which runs 718 funeral parlours and 39 crematoria, labelled 2015 as an "extraordinary year".
Chief executive Mike McCollum said: "It is impossible to talk about the group's performance in 2015 without discussing the almost unprecedented percentage increase in the number of deaths compared to 2014."
The firm said it was not in a position "to speculate on why this has happened", but regards this rise as a blip as it expects the death rate this year "to revert to the level seen in 2014."
It added the first two months of 2016 backed the "strong possibility the number of deaths in 2016 may be significantly lower than 2015." Shares fell more than 5%.
McCollum added: "Our staff have performed tremendously in a year when we had to look after a lot more families than originally anticipated."
During the year the business added 48 funeral locations to its network at a cost of £50m.
Its biggest single acquisition was its purchase of 36 parlours from Wolverhampton-based Laurel Funerals for £38m in June, which Dignity said have integrated well and performed in line with expectations.