Proper identification of urine crystals is essential in the routine mi
croscopic examination of urine sediment. Knowledge of structure, solub
ility, and pH characteristics of urine crystals comes with training an
d experience. References are available that provide excellent photogra
phs and illustrations to assist with recognition. In addition, these r
eferences provide guidelines far specialized testing or polarization c
haracteristics of specific urine crystals to further assist in identif
ication. Although crystals most often seen in urine generally are unre
lated to pathology and are considered Normal, they must be properly id
entified and reported because, occasionally they may have clinical sig
nificance. For example, calcium oxalate has been considered one of the
normal crystals, but it has been linked to lithiasis. This is the sec
ond article in a three-part continuing education update series on urin
alysis. Other articles in the series focus on urine sediment diagnosis
and urine cytodiagnostics.