Asthma guidelines suggest a stepwise approach to maintenance pharmacological treatment of persistent asthma until control is attained, and a 3 month review of the fixed maintenance dosing for step-up or step-down adjustment. This 12-week study compared the efficacy and safety of budesonide/formoterol in a single inhaler (Symbicort Turbuhaler 160/4.5 or 80/4.5 microg) given as adjustable maintenance or fixed maintenance dosing. Patients (n = 2358) were randomised to budesonide/formoterol fixed maintenance dosing (two inhalations bid) or adjustable maintenance dosing (two inhalation bid; stepping up to four inhalations bid if asthma worsened for a maximum of 14 days; stepping down to two inhalations once nocte or one inhalation bid if symptoms were controlled) for 12 weeks, following a 4-week run-in period on budesonide/formoterol two inhalations bid. Primary efficacy variables were frequency of asthma exacerbations and changes in patients' asthma symptom severity. Secondary variables were asthma control, safety and health economics. Both adjustable maintenance dosing and fixed maintenance dosing were associated with similar low frequency of exacerbations (5% both groups; ns) and similarly improved lung function, with similarly fewer nocturnal awakenings and less asthma symptoms compared with the mean value of the run-in period. However, patients on adjustable maintenance dosing used 24% fewer study drug compared with fixed maintenance dosing (2.95 versus 3.86 inhalations daily; p < 0.0001) and incurred in a significant (p <0.0001) reduction in total costs (direct+indirect) compared with fixed maintenance dosing. In conclusion, adjustable maintenance dosing with budesonide/formoterol effectively controls asthma at a reduced drug load with lower costs than fixed maintenance dosing.