The study was carried out by researchers from Dartmouth College in the US, and observed the habits of 3,000 10 to 14-year-olds over four years.
They found that children with a television in their bedroom gained weight at the rate of approximately one pound per year more than their peers without a TV in their room.
The link between the presence of a bedroom TV and faster weight gain held up even after researchers had controlled factors such as socio-economic status, education levels and parenting styles.
Researchers also warned that faster weight gain, particularly the 'belly fat' associated with sedentary TV viewing and the associated consumption of fatty, high-sodium snack food, meant a higher risk of developing diabetes and heart disease in later life.
However, although American paediatricians recommend limited 'screen time' for children - no more than two hours per day - a new study purports to show that giving children access to motion-sensing games consoles such as the Nintendo Wii and the Xbox Kinect increases their activity.
This study claims that, over a four-month period, overweight children who played these consoles lost twice as much weight as those enrolled on a weight management programme, suggesting that the link between screen-based entertainment and unhealthy lifestyles is far from clear-cut.