Loss‐of‐function experiments in mice have yielded invaluable mechanistic insights into the pathogenesis of Marfan syndrome (MFS) and implicitly, into the multiple roles fibrillin‐1 microfibrils play in the developing and adult organism. Unfortunately, neonatal death from aortic complications of mice lacking fibrillin‐1 (Fbn1^−/− mice) has limited the scope of these studies. Here, we report the creation of a conditional mutant allele (Fbn1^fneo) that contains loxP sites bordering exon1 of Fbn1 and an frt‐flanked neo expression cassette downstream of it. Fbn1^fneo/+ mice were crossed with FLPeR mice and the resulting Fbn1^Lox/+ progeny were crossed with Fbn1^+/−;CMV‐Cre mice to generate Fbn1^CMV−/− mice, which were found to phenocopy the vascular abnormalities of Fbn1^−/− mice. Furthermore, mating Fbn1^Lox/+ mice with Prx1‐Cre or Osx‐Cre mice revealed an unappreciated role of fibrillin‐1 microfibrils in restricting osteoprogenitor cell recruitment. Fbn1^Lox/+ mice are, therefore, an informative genetic resource to further dissect MFS pathogenesis and the role of extracellular fibrillin‐1 assemblies in organ development and homeostasis. genesis 50:635–641, 2012. © 2012 Wiley Periodicals, Inc.