An unusual urine color can occasionally be alarming to patient or physician. Abnormal urine color may indicate a range of normal or pathologic conditions. Variables that affect urine color include concentration, pH, ingested substances, and various metabolic abnormalities. Most causes can be determined by a careful history focusing on medications, foods, occupation, and family history. A few simple laboratory tests can confirm the diagnosis or narrow the list of possible causes. The evaluation should start with gross examination of the urine. Each abnormal color has a fairly limited differential diagnosis, which can be further narrowed by determining specific gravity and pH, and performing dipstick and microscopic examinations. The differential diagnosis can be narrowed further with ferric chloride or an ultraviolet (UV) light source. Rarely, more specific tests are useful. We present an algorithm that may be of benefit in the logical, inexpensive, and efficient evaluation of abnormal urine color.