A vascular implant formed of a compressible foam material has a compressed configuration from which it is expansible into a configuration substantially conforming to the shape and size of a vascular site to be embolized. Preferably, the implant is formed of a hydrophilic, macroporous foam material, having an initial configuration of a scaled-down model of the vascular site, from which it is compressible into the compressed configuration. The implant is made by scanning the vascular site to create a digitized scan data set; using the scan data set to create a three-dimensional digitized virtual model of the vascular site; using the virtual model to create a scaled-down physical mold of the vascular site; and using the mold to create a vascular implant in the form of a scaled-down model of the vascular site. To embolize a vascular site, the implant is compressed and passed through a microcatheter, the distal end of which has been passed into a vascular site. Upon entering the vascular site, the implant expands in situ substantially to fill the vascular site. A retention element is contained within the microcatheter and has a distal end detachably connected to the implant. A flexible, tubular deployment element is used to pass the implant and the retention element through the microcatheter, and then to separate the implant from the retention element when the implant has been passed out of the microcatheter and into the vascular site.