OBJECTIVES: Empirical studies show a severe undertreatment of patients with Alzheimer's disease in Germany. This comparative online panel survey investigates potential causes for undertreatment among general practitioners (GPs) and neurologists/psychiatrists. METHODS: A total of 100 neurologists/psychiatrists and 302 GPs were included in an online panel survey. Participating GPs had experiences in treating diabetes, asthma, depression, epilepsy, migraine and dementia; neurologists were experienced in schizophrenia, depression, epilepsy, multiple sclerosis, migraine and dementia. Participants were asked to compare these therapeutic areas in 8 items: urgency of treatment, therapeutic options, difficulties in diagnosis, knowledge on guidelines, difficulties in patient and care-giver communication, influence of budget restrictions, experiences in switching therapy and referrals to specialists. A Likert-rating scale (1-5) was used for assessing. An additional open question addressed reasons for discontinuing therapy with antidementive drugs. RESULTS: For Alzheimer's disease GPs see lowest urgency for treatment (2.2; 1.3 in diabetes), lowest number of therapeutic options (3.5; 1.5 in asthma), largest difficulties in diagnosis (3.3; 1.7 in diabetes), largest difficulties in patient and care-giver communication (3.7; 1.9 in diabetes) and highest budget restrictions (2.0; 2.8 in epilepsy). GPs' knowledge of guidelines is lowest in epilepsy (3.4) and dementia (3.0; 1.7 in diabetes); their experience in therapeutic switches is lowest, the number of referrals to specialists highest. Neurologists agree with GPs that therapeutic options in dementia are lowest (3.5, 1.5 in schizophrenia) and budget pressure is highest (1.9; 2.7 in epilepsy). They see a higher urgency of treatment for Alzheimer and show more experience in treatment. Both groups agreed that budget restraints are the most important reason for discontinuing treatment with antidementive drugs. CONCLUSIONS: Results suggest that budget constraints for GPs and neurologists/psychiatrists are the dominant reason for undertreatment of patients with Alzheimer's disease. To ensure evidence-based treatment with antidementive drugs in Germany budget constraints need to be reduced.