We examined the relationship between recognition of a 3-kg weight gain in 1 year with metabolic syndrome parameters and lifestyle status related to metabolic syndrome or cardiovascular disease in Japanese workers. Data were collected twice between April 2009 and March 2011, and self-reported questionnaires were completed at a follow-up by 275 workers who gained more than 3 kg in 1 year. This study showed that ~40 per cent of those who gained more than 3 kg in a year did not recognise their weight gain, and a weight gain over 3 kg was associated with worse metabolic syndrome parameters regardless of weight gain recognition.