The continuing progress of sub-65 nm patterning technologies highlights the critical need for high precision metrologies capable of characterizing dense, high aspect ratio patterns. We present data from small angle x-ray scattering measurements of critical dimension and average pattern cross section of photoresist line/space patterns. The technique is non-destructive and capable of sub-nm precision in characterizing dimensions and sub-degree precision in sidewall angle of patterns with regular periodicity. Moreover, the information enabling linewidth, pitch and sidewall angle determination are decoupled. Efforts to probe line edge roughness are also discussed. The technique is applicable to dense structures of arbitrary composition with dimensions of (10 to 500) nm, including lines, vias and contact holes and buried structures.