Background: Although respiratory allergies to house dust mites (HDMs) can often be controlled with symptomatic medications, some patients do not achieve satisfactory disease control. Objective: To assess fortnightly fluctuations (notably worsening and/or exacerbations) in disease parameters among patients taking only symptomatic medications for HDM allergy. Methods: In a 13-month, observational, multicenter survey of adults with a self-reported history of poorly controlled, moderate-to-severe, physician-diagnosed HDM respiratory allergy in France, Italy, and Spain, fortnightly telephone interviews were used to gather information on medication use, symptoms, the disease burden, and medical consultations from late May 2012 to early July 2013. Results: A total of 313 patients completed the study (n = 114 in Italy, 92 in France, and 107 in Spain). Although most participants reported improvements in symptoms, a substantial minority (ranging from 12% to 44% per fortnightly telephone interview in 2012 and from 16% to 37% in 2013) complained of worsening. A few study participants did not improve at any time in the study: 4% overall, and 2%, 2%, and 7% in Italy, France and Spain, respectively. A change in the weather and/or contact with other allergens were the most frequent self-reported reasons for worsening, although the answer "I don't know" was also prominent. Conclusion: In a 13-month survey of patients with HDM allergy in Italy, France, and Spain, the participants' symptom status fluctuated significantly - illustrating the complexity of this condition. Although most participants reported improvements, the "never-improver" profile warrants further investigation. More prominence could be given to symptom control and a low exacerbation risk as treatment goals in allergic rhinitis.