We demonstrate recovery of optical properties using arrays of interstitial cylindrical diffusing fibers as sources and detectors. A single 1-cm diffuser delivered laser illumination at 665 nm, while seven 1- and 2-cm diffusers at 1-cm grid spacing acted as detectors. Extraction of optical properties from these measurements was based upon a diffusion model of emission and detection distributions for these diffuser fibers, informed by previous measurements of heterogeneous axial detection. Verification of the technique was performed in 15 liquid tissue-simulating phantoms consisting of deionized water, India ink as absorber, and Intralipid 20% as scatterer. For the range of optical properties tested, mean errors were 4.4% for effective attenuation coefficient, 12.6% for absorption coefficient, and 7.6% for reduced scattering coefficient. Error in recovery tended to increase with decreasing transport albedo. For therapeutic techniques involving the delivery of light to locations deep within the body, such as interstitial photodynamic and photothermal therapies, the methods described here would allow the treatment diffuser fibers also to be used as sources and detectors for recovery of optical properties. This would eliminate the need for separately inserted fibers for spectroscopy, reducing clinical complexity and improving the accuracy of treatment planning.