Does the insomnia drug Ambien show up in a drug test? If so, how long
is it present urine?

It is possible that Ambien (zolpidem) may cause a false-positive
result for benzodiazepines (drugs such as Valium and Xanax). Ambien is
not actually a benzodiazepine, but it shares some pharmacological
properties with the benzodiazepines.

"Ambien has been known... to cause a false positive for
Benzodiazepines. While it is in the drug Class Hypnotics, it is still
a schedual IV Narcotic DEA number 2783 controlled substance. Depending
on the testing methods it will show up."

Rxlist Messageboard: Bendodiaziapines & Drug Testing 
http://www.rxlist.com/rxboard/ambien.pl?read=1055

Regarding the matter of how long Ambien is detectable, the drug is
rapidly eliminated from the body, and is usually undetectable within 6
to 14 hours.

This comes from a question-and-answer site sponsored by Oregon State
University's Student Health Services:

"Q: how long does ambien stay in system

 A: The elimination half-life of Ambien (zolpiden) is 1.4 to 2.2
hours. This should mean that it is undetectable after 8.4 to 13.2
hours from the last dose."

http://studenthealth.oregonstate.edu/AnswerSPOT/AlcoholDrugs/DrugTesting%20&%20Metabolism/AD_Test_0358.htm

This is from the Journal of the Wisconsin Medical Society:

"Zolpidem has a short half-life, causing it to be completely
eliminated from the bloodstream within 8 hours, so as not to be
present during hours of activity."

Wisconsin Medical Journal: Forensic Toxicology Program
http://www.wisconsinmedicalsociety.org/uploads/wmj/HardingSA.pdf

From a fact sheet on zolpidem:

"The elimination half-life is short, with a mean of 2.4 hours and a
duration of action up to 6 hours.

All metabolites are pharmacologically inactive and are eliminated in
the urine (56%) and in the faeces (37%)."

Medical Products Agency: Summary of Product Characteristics
http://www.mpa.se/spc_pil/pdf/enhumspc/Zolpidem%20NM%20Pharma%20tabl%20%20ENG.pdf

It should be mentioned that there is a specific (and expensive) assay
which can detect zolpidem in blood or urine up to 48 hours after
ingestion. This kind of test is highly unlikely to be used in mass
drug-screening, but can be applied to certain forensic and medical
purposes:

"The development of a specific and sensitive radioimmunoassay for the
detection of zolpidem and its metabolites in urine and serum samples
is described... Using this assay, zolpidem levels were determined in
urine and serum, and could be easily detected up to 48 h after oral
intake of 10 mg of zolpidem."

PubMed: Development of a radioimmunoassay for the determination of
zolpidem in biological samples.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9463966&dopt=Abstract

Google search strategy:

Google Web Search: ambien OR zolpidem "drug test OR tests OR testing"
://www.google.com/search?hl=en&ie=UTF-8&q=ambien+OR+zolpidem+%22drug+test+OR+tests+OR+testing

Google Web Search: zolpidem OR ambien urine OR urinalysis
://www.google.com/search?hl=en&ie=UTF-8&q=zolpidem+OR+ambien+urine+OR+urinalysis

I hope this helps! If anything is unclear, or if a link doesn't work
for you, please request clarification; I'll be glad to offer further
assistance before you rate my answer.

Best regards,
pinkfreud