Background context: It is generally recognized that long periods of sitting can either cause or aggravate lumbar pain. A new, ergonomically designed chair has a fixed backrest and a motor-driven seat with a horizontal rotary movement in alternating left-right cycles. Purpose: The objective of this study is to prove superiority of the new technique of passive rotary dynamic sitting for subjects working in a sedentary occupation and suffering from lumbar pain. Study design/setting: A randomized, double-blind, multicenter, two-armed study was performed using a parallel group design. Patient sample: 280 persons suffering from lumbar pain were matched pairwise and randomized en bloc. Outcome measures: The first and second primary endpoints target criteria were the validated German version of the Oswestry Disability Index (ODI) and the number of days of absence from work (DA) attributable to lumbar pain, each based on a blinded 2-year follow-up observation after randomization of the subjects. Methods: After inclusion in the study anonymization, the probands were randomized to receive either an office chair with a motor-driven seat performing a horizontal rotary movement or a chair of the same design without the rotary seat movement. Before delivery of the chairs, 23 probands (8.2%) withdrew their consent to inclusion in the study without stating reasons. From 12 of the remaining matching partners, 23 new pairs were created at random, and the study commenced with 124 pairs. Results: A further 27 probands (9.6%) were lost to follow-up during the period up to the final consultation. This made it possible to observe the primary endpoint in 82.5% of the probands. The median ODI in both groups was 53 (95% confidence interval for median difference:-1.5 to 0.5; p=.59). Median DA in both groups was 0 (95% confidence interval for median difference:-∞-+∞; p=1.00). Conclusions: Under the test conditions used in this study, passive rotary dynamic sitting was not superior to sitting in a high-quality, ergonomically designed chair not equipped with a micro-rotation function in patients suffering from lumbar pain.