Lyme borreliosis (LB) is the most frequent vector-borne disease in Germany. For more than 10 years, data from mandatory notifications have been available from 6 federal states in the eastern part of Germany. A common case definition was applied. Clinical manifestations of erythema migrans, neuroborreliosis (radiculoneuritis, cranial neuritis, meningitis), and Lyme arthritis were notifiable. From 2009 to 2012, altogether 18,894 cases were notified. The overall incidence varied between 34.9 cases/100,000 inhabitants in 2009 and 19.54 cases/100,000 persons in 2012. LB in eastern Germany showed a pronounced seasonality with a peak in August. Decreasing as well as increasing trends were observed in different federal states. Females predominated among all cases (55.3%). The age distribution was bimodal with incidence peaks in children 5-9 years old (32.4 cases/100,000 persons in 2011) and in adults aged 60-69 years (56.7 cases/100,000 persons in 2011). Erythema migrans affected 95.4% of the patients and acute neuroborreliosis 3.3%. Among the latter, the most common manifestation was radiculoneuritis (n=316). Neuritis cranialis was more common in children than in adults (p<0.01). The same was true for meningitis (p<0.01). Altogether 2.0% of the LB cases developed Lyme arthritis. LB has a significant disease burden in the study area. Different levels of under-ascertainment in the surveillance system could explain parts of the differences in the incidence. Furthermore, there may be discrepancies in disease awareness among patients and physicians. Changes in time and differences among geographical regions could result from variations in risk factors related to human behaviour (e.g., outdoor activity). Additionally, vector-related risk factors may have varied (e.g., landscape, climate). Public health strategies with a particular focus on the high-incidence age groups should promote daily checks for ticks and prompt removal of ticks after exposure to avoid infection. Physicians should be able to recognize LB patients with early manifestations and promptly treat those appropriately.