This study describes the main characteristics of ongoing observational studies on Alzheimer's disease (AD) to help identify any important research gaps. A search through the WHO International Clinical Trials Registry Platform and on the Primary Registries was conducted on 9 June 2012. The descriptors 'recruiting' or 'open' were used to describe a study's recruitment status. 62 studies are being conducted in 18 countries (Australia, Far-East, Middle-East, North America, and Western Europe). The US and France are involved in 55% of these studies. The studies aimed to recruit 20 to 10,000 participants, lasting 8 months to 24 years; 46% are case-control, whereas 44% are cohort studies; 60% and 34% are longitudinal and cross-sectional, respectively. The majority are sponsored by hospitals, universities, medical centers, or public health systems (63%), and are conducted in single centers (55%). 37 use imaging (MRI, PET, SPECT), 18 conduct lumbar puncture, 21 collect DNA and/or RNA, and 15 collect ApoE genotyping. 17 studies are medium-term prospective disease progression studies, the majority to assess mild cognitive impairment (MCI) or/and AD progression; only 3 are on cognitively normal older people at risk (2 studies, n = 180) or not (1 study, n < 200) of developing MCI. Observational studies are being conducted in few countries, with very few in low and middle-income countries where the majority of AD patients live. There is a remarkable interest in disease progression studies; however, longitudinal, long-term studies, on cognitively normal middle-age individuals, of key importance to try to fully understand the preclinical phase of AD, are lacking.