Self-efficacy is a temporary and influenceable characteristic, related to situations and tasks, mediating health-promoting behaviours. This study aimed to evaluate psychometric properties of a Portuguese version of the Fluid Intake Appraisal Inventory, and to describe self-efficacy in relation to limited fluid intake amongst Portuguese haemodialysis patients. Respondents were recruited from three dialysis units, and 113 of 155 eligible patients gave their informed consent. The translated scale was distributed and collected by the head nurses. Interdialytic weight gain was calculated as percentage of dry weight. Satisfactory psychometric properties were estimated in the Portuguese context. The participants' self-efficacy in relation to low fluid intake was asymmetrically distributed; the majority had moderately to high self-efficacy while some patients had very low self-efficacy to limited fluid intake. There was a significant difference in self-efficacy to fluid restrictions; patients with a weight gain of 3.5% or less presented higher self-efficacy scores than did patients exceeding the cutoff point.