The number of cot deaths in England and Wales fell by 15% between 2004 and 2005, provisional figures show.
Putting a baby to sleep on its back reduces the risk of cot death
Data from the Office for National Statistics show the rate fell from 0.48 to 0.41 deaths per 1,000 live births.
The figures also show that, between 2001 and 2005, boys made up 58% of cot deaths despite making up only 51% of all live births.
In 2005, the cot death rate was highest for babies born outside marriage where only the mother registered the birth.
HOW TO CUT THE RISK
Cut out smoking during pregnancy
Fathers should stop smoking at this time too
Do not let anyone smoke in the same room as your baby
Place your baby on its back to sleep
Do not let your baby get too hot
Keep your baby's head uncovered
Place your baby with its feet to the foot of the cot
Preferably sleep your baby in a cot in your bedroom for the first six months
Do not sleep with a baby on a sofa, armchair or settee
If your baby is unwell, seek medical advice promptly
The rate for this group was 1.20 per 1,000 live births - six times higher than the rate for babies born inside marriage (0.19 per 1,000).
Between 2001 and 2005, 63% of all unexplained deaths occurred in babies aged less than three months.
For babies born within marriage, the unexplained infant death rate increased with number of previous births.
In 2005, the rate for babies of mothers with two or more previous births (0.34 per 1,000 live births) was three times the rate of babies with no previous births (0.10 per 1,000).
It is thought that the fall in cot deaths is at least partly due to wide dissemination of advice about how to minimise the risk.
It is part of a continuing trend - numbers of cot deaths have fallen from 377 to 300 since 2001.
However, there has been no fall in the total infant or post neonatal infant mortality rate.
This suggests that better investigation is defining the cause of death in more babies.
Dr Richard Wilson, a paediatrician and trustee of the Foundation for the Study of Infant Deaths, said more research was needed into the causes of cot death.
He said: "Every year 300 apparently healthy babies die suddenly and unexpectedly in the UK.
"If the same number of people were involved annually in a fatal plane or train crash there would be outrage and investigations.
"Research has revealed some of the ways to reduce the risk of cot death but the causes of most of these tragedies remain unknown.
"Bereaved parents ask us the all-consuming question of 'why did my baby die?' and they deserve answers."