Facebook has denied that it is losing clients, saying it is "pleased" with growth.
Digits from Facebook's monitoring site Inside Facebook suggested that during May, Facebook missed six million users in the US and 100,000 in the UK.
But the social network, which does not usually comment on third party statistics, wondered how it arrived at this figure.
"From time to time, we see stories about Facebook losing users in some regions. Some of these reports use data extracted from our advertising tool, which provides broad estimates on the reach of Facebook ads and isn't designed to be a source for tracking the overall growth of Facebook," the firm said in a statement.
"We are very pleased with our growth and with the way people are engaged with Facebook. More than 50% of our active users log on to Facebook in any given day," it added.
The figures from Inside Facebook also claimed that 1.5 million Canadian users left the social network in May.
But in overall it showed that Facebook was growing, to a total of 687 million users worldwide with numerous customers coming from countries such as India, the Philippines and Indonesia.
Its digits on customer outflow do not appear to tally with those from net measurement firm comScore, according to BBC.