More women than men were killed by the Asian tsunami, Oxfam figures from India, Indonesia and Sri Lanka suggest.
In some regions the disaster claimed four times as many women as men.
The charity says women were worst-hit because they were waiting on beaches for fishermen to return, or at home looking after children at the time.
The research comes exactly three months after the under-sea earthquake caused a wave that devastated coastlines around the Indian Ocean.
Oxfam International focused their research on the Indonesian province of Aceh, the Cuddalore district of India, and took data from camps across Sri Lanka.
In four villages in Aceh Besar district only 189 of 676 survivors were female - men outnumbering women three to one.
'Disproportionate impact'
In four villages in North Aceh district, 82 men died, compared to 284 women.
A staggering 80% of those who died in Kuala Cangkoy in North Aceh were women.
"This disproportionate impact will lead to problems for years to come unless everyone working on the aid effort addresses the issue now"
India suffered a similar fate with three times as many women being killed as men in Cuddalore district - the second most seriously affected area in India.
In one Indian village, Pachaankuppam, the only people who died were female.
The story is the same for Sri Lanka where the number of male survivors in the emergency camps far outweigh the women.
Becky Buell, Oxfam's policy director, said the tsunami had dealt a "crushing blow" to both women and men.
"This disproportionate impact will lead to problems for years to come unless everyone working on the aid effort addresses the issue now."
She said there are already reports of rapes, harassment and forced marriages coming from emergency camps around the region.
She urged people to "wake up" to the issue and ensure "protection, inclusion and empowerment" of female survivors.
Errands
The report suggested a number of reasons for the high proportion of female deaths.
On the Indian coast many women were waiting for the fishermen to return with their catches, while in Batticaloa on the east coast of Sri Lanka, the tsunami hit at the exact moment many of the women were taking baths in the sea.
Because it was a Sunday, many of the women in Aceh were at home with the children rather than at work.
The men in most parts of Aceh were either carrying out errands or in their boats out at sea, where the waves were less ferocious.
Ms Buell called on governments and NGOs to help ensure women are given the same opportunities as men to rebuild their lives.
She added it is important to work with men who had lost their wives and teach them how to care properly for their children.
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