We describe a new locality with microdiamond-bearing, ultrahigh-pressure metamorphic rocks near the village Sidironero in the Rhodope Metamorphic Province in northern Greece, about 70 km west of the nearest known location at Xanthi. High- and ultrahigh-pressure metamorphic conditions are preserved in an intensely strained mélange zone which is sandwiched between upper-greenschist to lower-amphibolite-facies rocks in the footwall (Pangaion-Pirin Complex) and upper-amphibolite-facies rocks in the hanging wall (Rhodope Terrane). The mélange zone consists of various paragneisses, orthogneisses and metamafics. A strong overprint at upper-amphibolite-facies conditions associated with migmatisation in the orthogneisses and subsequent intense mylonitisation at lower-amphibolite-facies conditions almost obliterates peak-pressure assemblages. Relics of high-pressure conditions are preserved in mafic boudins and in garnet-kyanite-mica schists. Garnet in garnet-kyanite-mica schists displays inclusions of microdiamonds and swarms of non-oriented rods of rutile and quartz. The lithological and structural appearance of the mélange zone resembles the exposure of ultrahigh-pressure metamorphic rocks further east at Xanthi, whereas the location at Kimi may occupy a higher structural level.