1.1 cm bilat persistent neck lymph node in healthy child w/ cmv igg186 ua; igm neg. us=reactive, cbc/hsr normal. 4weeks, no increasing. need follow up?

No: Keep an eye on it, and if your physician is not concerned, i wouldn't be either. Depending on location, this may actually be a little cyst.

Always good : To have an enlarged lymph node followed up. Depends on other circumstances, signs and symptoms associated with it, your physician will want to see you sooner or monitor you once a year or have you come in sooner if condition has changed.Sounds more like reactive lymphadenopathy due to past infections- viral , strep throat, skin infections etc it may take time to resolve.