The editorial team has chosen the paper by Rockwood and colleagues on good and bad days in dementia, which immediately follows this commentary in this current issue of International Psychogeriatrics, to be the paper of the month.

When I was an intern I learned at first hand that fluctuation is intrinsic (Siddiqi et al., Reference Siddiqi, House and Holmes2006; Collins et al., Reference Collins, Blanchard, Tookman and Sampson2010) to the nature of delirium (I would be told coming on duty at 7.30 am that a patient had been “right off” overnight, but when I went to see her, she would appear to be quite alright – yet the nurses were giving me accurate reports of her overnight state). Later I learned that patients affected by dementia with Lewy bodies (DLB) were meant to show fluctuating symptoms too and, indeed, many of those whom I recognized that I was looking after, following the emergence and promulgation of diagnostic criteria in the early 1990s, did indeed seem to show marked symptomatic fluctuation (Yeatman et al., Reference Yeatman, McLean and Ames1994). But some patients with dementia which seems to be due to Alzheimer's disease (AD), cerebrovascular disease (CVD), or some combination of the two, are reported by their families to show symptom fluctuation from day to day too, despite lacking the spontaneous motor Parkinsonism and visual hallucinations that they ought to display if DLB were the main cause of their decline. Now Rockwood and colleagues have taken a group of patients affected by dementia due to AD and mixed AD and CVD and have shown pretty clearly that clinically significant variability in symptoms is quite common, even though “what makes a day ‘good’ is not simply more (or less) of what makes a day ‘bad.’” Perhaps one implication of this work is that we should stop worrying about the inevitable diagnostic flip-flopping, which is prone to occur in patients initially diagnosed with Mild Cognitive Impairment (Ellis et al., Reference Ellis2014), while another is that we should explain to both patients and families that cognitive fluctuation may occur and undertake more research that can tell us what to say when they ask us how to cope with these changes.